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Topics Covered In This Chapter:

This game introduces many new concepts. But don't worry; we'll experiment with these programming concepts in the interactive shell first. Some data types such as strings and lists have functions that are associated with their values called methods. We will learn several different methods that can manipulate strings and lists for us. We will also learn about a new type of loop called a for loop and a new type of data type called a dictionary. Once you understand these concepts, it will be much easier to understand the game in this chapter: Hangman.

You can learn more from Wikipedia: http://en.wikipedia.org/wiki/Hangman_(game)

Hangman's Source Code

This chapter's game is a bit longer than our previous games. You can either type in the code below directly into the file editor (which I recommend) or you can obtain the code from this book's website. To grab the code from the web, in a web browser go to the URL http://inventwithpython.com/chapter9 and follow the instructions for downloading the source code.

hangman.py
This code can be downloaded from http://inventwithpython.com/hangman.py
If you get errors after typing this code in, compare it to the book's code with the online diff tool at http://inventwithpython.com/diff or email the author at [email protected]

  1. import random
  2. HANGMANPICS = ['''
  3.   +---+
  4.   |   |
  5.       |
  6.       |
  7.       |
  8.       |
  9. =========''', '''
  10.   +---+
  11.   |   |
  12.   O   |
  13.       |
  14.       |
  15.       |
  16. =========''', '''
  17.   +---+
  18.   |   |
  19.   O   |
  20.   |   |
  21.       |
  22.       |
  23. =========''', '''
  24.   +---+
  25.   |   |
  26.   O   |
  27.  /|   |
  28.       |
  29.       |
  30. =========''', '''
  31.   +---+
  32.   |   |
  33.   O   |
  34.  /|\  |
  35.       |
  36.       |
  37. =========''', '''
  38.   +---+
  39.   |   |
  40.   O   |
  41.  /|\  |
  42.  /    |
  43.       |
  44. =========''', '''
  45.   +---+
  46.   |   |
  47.   O   |
  48.  /|\  |
  49.  / \  |
  50.       |
  51. =========''']
  52. words = 'ant baboon badger bat bear beaver camel cat clam cobra cougar coyote crow deer dog donkey duck eagle ferret fox frog goat goose hawk lion lizard llama mole monkey moose mouse mule newt otter owl panda parrot pigeon python rabbit ram rat raven rhino salmon seal shark sheep skunk sloth snake spider stork swan tiger toad trout turkey turtle weasel whale wolf wombat zebra'.split()
  53. def getRandomWord(wordList):
  54.     # This function returns a random string from the passed list of strings.
  55.     wordIndex = random.randint(0, len(wordList) - 1)
  56.     return wordList[wordIndex]
  57. def displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord):
  58.     print(HANGMANPICS[len(missedLetters)])
  59.     print()
  60.     print('Missed letters:', end=' ')
  61.     for letter in missedLetters:
  62.         print(letter, end=' ')
  63.     print()
  64.     blanks = '_' * len(secretWord)
  65.     for i in range(len(secretWord)): # replace blanks with correctly guessed letters
  66.         if secretWord[i] in correctLetters:
  67.             blanks = blanks[:i] + secretWord[i] + blanks[i+1:]
  68.     for letter in blanks: # show the secret word with spaces in between each letter
  69.         print(letter, end=' ')
  70.     print()
  71. def getGuess(alreadyGuessed):
  72.     # Returns the letter the player entered. This function makes sure the player entered a single letter, and not something else.
  73.     while True:
  74.         print('Guess a letter.')
  75.         guess = input()
  76.         guess = guess.lower()
  77.         if len(guess) != 1:
  78.             print('Please enter a single letter.')
  79.         elif guess in alreadyGuessed:
  80.             print('You have already guessed that letter. Choose again.')
  81.         elif guess not in 'abcdefghijklmnopqrstuvwxyz':
  82.             print('Please enter a LETTER.')
  83.         else:
  84.             return guess
  85. def playAgain():
  86.     # This function returns True if the player wants to play again, otherwise it returns False.
  87.     print('Do you want to play again? (yes or no)')
  88.     return input().lower().startswith('y')
  89. print('H A N G M A N')
  90. missedLetters = ''
  91. correctLetters = ''
  92. secretWord = getRandomWord(words)
  93. gameIsDone = False
  94. while True:
  95.     displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)
  96.     # Let the player type in a letter.
  97.     guess = getGuess(missedLetters + correctLetters)
  98.     if guess in secretWord:
  99.         correctLetters = correctLetters + guess
  100.         # Check if the player has won
  101.         foundAllLetters = True
  102.         for i in range(len(secretWord)):
  103.             if secretWord[i] not in correctLetters:
  104.                 foundAllLetters = False
  105.                 break
  106.         if foundAllLetters:
  107.             print('Yes! The secret word is "' + secretWord + '"! You have won!')
  108.             gameIsDone = True
  109.     else:
  110.         missedLetters = missedLetters + guess
  111.         # Check if player has guessed too many times and lost
  112.         if len(missedLetters) == len(HANGMANPICS) - 1:
  113.             displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)
  114.             print('You have run out of guesses!\nAfter ' + str(len(missedLetters)) + ' missed guesses and ' + str(len(correctLetters)) + ' correct guesses, the word was "' + secretWord + '"')
  115.             gameIsDone = True
  116.     # Ask the player if they want to play again (but only if the game is done).
  117.     if gameIsDone:
  118.         if playAgain():
  119.             missedLetters = ''
  120.             correctLetters = ''
  121.             gameIsDone = False
  122.             secretWord = getRandomWord(words)
  123.         else:
  124.             break

How the Code Works

  1. import random

The Hangman program is going to randomly select a secret word from a list of secret words. This means we will need the random module imported.

  1. HANGMANPICS = ['''
  2.   +---+
  3.   |   |
  4.       |
  5.       |
  6.       |
  7.       |
  8. =========''', '''

...the rest of the code is too big to show here...

This "line" of code is a simple variable assignment, but it actually stretches over several real lines in the source code. The actual "line" doesn't end until line 58. To help you understand what this code means, you should learn about multi-line strings and lists:

Multi-line Strings

Ordinarily when you write strings in your source code, the string has to be on one line. However, if you use three single-quotes instead of one single-quote to begin and end the string, the string can be on several lines:

>>> fizz = '''Dear Alice,
I will return home at the end of the month. I will see you then.
Your friend,
Bob'''
>>> print(fizz)
Dear Alice,
I will return home at the end of the month. I will see you then.
Your friend,
Bob
>>>

If we didn't have multi-line strings, we would have to use the \n escape character to represent the new lines. But that can make the string hard to read in the source code, like in this example:

>>> fizz = 'Dear Alice,\nI will return home at the end of the month. I will see you then.\nYour friend,\nBob'
>>> print(fizz)
Dear Alice,
I will return home at the end of the month. I will see you then.
Your friend,
Bob
>>>

Multi-line strings do not have to keep the same indentation to remain in the same block. Within the multi-line string, Python ignores the indentation rules it normally has for where blocks end.

def writeLetter():
    # inside the def-block
    print('''Dear Alice,
How are you? Write back to me soon.

Sincerely,
  Bob''') # end of the multi-line string and print() call
    print('P.S. I miss you.') # still inside the def-block

writeLetter() # This is the first line outside the def-block.

Constant Variables

You may have noticed that HANGMANPICS's name is in all capitals. This is the programming convention for constant variables. Constants are variables whose values do not change throughout the program. Although we can change HANGMANPICS just like any other variable, the all-caps reminds the programmer to not write code that does so.

Constant variables are helpful for providing descriptions for values that have a special meaning. Since the multi-string value never changes, there is no reason we couldn't copy this multi-line string each time we needed that value. The HANGMANPICS variable never varies. But it is much shorter to type HANGMANPICS than it is to type that large multi-line string.

Also, there are cases where typing the value by itself may not be obvious. If we set a variable eggs = 72, we may forget why we were setting that variable to the integer 72. But if we define a constant variable DOZEN = 12, then we could set eggs = DOZEN * 6 and by just looking at the code know that the eggs variable was set to six dozen.

Like all conventions, we don't have to use constant variables, or even put the names of constant variables in all capitals. But doing it this way makes it easier for other programmers to understand how these variables are used. (It even can help you if you are looking at code you wrote a long time ago.)

Lists

I will now tell you about a new data type called a list. A list value can contain several other values in it. Try typing this into the shell: ['apples', 'oranges', 'HELLO WORLD']. This is a list value that contains three string values. Just like any other value, you can store this list in a variable. Try typing spam = ['apples', 'oranges', 'HELLO WORLD'], and then type spam to view the contents of spam.

>>> spam = ['apples', 'oranges', 'HELLO WORLD']
>>> spam
['apples', 'oranges', 'HELLO WORLD']
>>>

Lists are a good way to store several different values into one variable. The individual values inside of a list are also called items. Try typing: animals = ['aardvark', 'anteater', 'antelope', 'albert'] to store various strings into the variable animals. The square brackets can also be used to get an item from a list. Try typing animals[0], or animals[1], or animals[2], or animals[3] into the shell to see what they evaluate to.

>>> animals = ['aardvark', 'anteater', 'antelope', 'albert']
>>> animals[0]
'aardvark'
>>> animals[1]
'anteater'
>>> animals[2]
'antelope'
>>> animals[3]
'albert'
>>>

The number between the square brackets is the index. In Python, the first index is the number 0 instead of the number 1. So the first item in the list is at index 0, the second item is at index 1, the third item is at index 2, and so on. Lists are very good when we have to store lots and lots of values, but we don't want variables for each one. Otherwise we would have something like this:

>>> animals1 = 'aardvark'
>>> animals2 = 'anteater'
>>> animals3 = 'antelope'
>>> animals4 = 'albert'
>>>

This makes working with all the strings as a group very hard, especially if you have hundreds or thousands (or even millions) of different strings that you want stored in a list. Using the square brackets, you can treat items in the list just like any other value. Try typing animals[0] + animals[2] into the shell:

>>> animals[0] + animals[2]
'aardvarkantelope'
>>>

Because animals[0] evaluates to the string 'aardvark' and animals[2] evaluates to the string 'antelope', then the expression animals[0] + animals[2] is the same as 'aardvark' + 'antelope'. This string concatenation evaluates to 'aardvarkantelope'.

What happens if we enter an index that is larger than the list's largest index? Try typing animals[4] or animals[99] into the shell:

>>> animals = ['aardvark', 'anteater', 'antelope', 'albert']
>>> animals[4]
Traceback (most recent call last):
File "", line 1, in
animals[4]
IndexError: list index out of range
>>> animals[99]
Traceback (most recent call last):
File "", line 1, in
animals[99]
IndexError: list index out of range
>>>

If you try accessing an index that is too large, you will get an index error.

Changing the Values of List Items with Index Assignment

You can also use the square brackets to change the value of an item in a list. Try typing animals[1] = 'ANTEATER', then type animals to view the list.

>>> animals = ['aardvark', 'anteater', 'antelope', 'albert']
>>> animals[1] = 'ANTEATER'
>>> animals
['aardvark', 'ANTEATER', 'antelope', 'albert']
>>>

The second item in the animals list has been overwritten with a new string.

List Concatenation

You can join lists together into one list with the + operator, just like you can join strings. When joining lists, this is known as list concatenation. Try typing [1, 2, 3, 4] + ['apples', 'oranges'] + ['Alice', 'Bob'] into the shell:

>>> [1, 2, 3, 4] + ['apples', 'oranges'] + ['Alice', 'Bob']
[1, 2, 3, 4, 'apples', 'oranges', 'Alice', 'Bob']
>>>

Notice that lists do not have to store values of the same data types. The example above has a list with both integers and strings in it. Remember, when you do list concatenation, you must add together two list values. ['apples'] + ['oranges'] will evaluate to ['apples', 'oranges']. But ['apples'] + 'oranges' will result in an error because you are adding a list value and string value instead of two list values. If you want to add non-list values to a list, use the append() method (which is described later).

The in Operator

The in operator makes it easy to see if a value is inside a list or not. Expressions that use the in operator return a Boolean value: True if the value is in the list and False if the value is not in the list. Try typing 'antelope' in animals into the shell:

>>> animals = ['aardvark', 'anteater', 'antelope', 'albert']
>>> 'antelope' in animals
True
>>>

The expression 'antelope' in animals returns True because the string 'antelope' can be found in the list, animals. (It is located at index 2.)

But if we type the expression 'ant' in animals, this will return False because the string 'ant' does not exist in the list. We can try the expression 'ant' in ['beetle', 'wasp', 'ant'], and see that it will return True.

>>> animals = ['aardvark', 'anteater', 'antelope', 'albert']
>>> 'antelope' in animals
True
>>> 'ant' in animals
False
>>> 'ant' in ['beetle', 'wasp', 'ant']
True
>>>

The in operator also works for strings as well as lists. You can check if one string exists in another the same way you can check if a value exists in a list. Try typing 'hello' in 'Alice said hello to Bob.' into the shell. This expression will evaluate to True.

>>> 'hello' in 'Alice said hello to Bob.'
True
>>>

Removing Items from Lists with del Statements

You can remove items from a list with a del statement. ("del" is short for "delete.") Try creating a list of numbers by typing: spam = [2, 4, 6, 8, 10] and then del spam[1]. Type spam to view the list's contents:

>>> spam = [2, 4, 6, 8, 10]
>>> del spam[1]
>>> spam
[2, 6, 8, 10]
>>>

Notice that when you deleted the item at index 1, the item that used to be at index 2 became the new value at index 1. The item that used to be at index 3 moved to be the new value at index 2. Everything above the item that we deleted moved down one index. We can type del spam[1] again and again to keep deleting items from the list:

>>> spam = [2, 4, 6, 8, 10]
>>> del spam[1]
>>> spam
[2, 6, 8, 10]
>>> del spam[1]
>>> spam
[2, 8, 10]
>>> del spam[1]
>>> spam
[2, 10]
>>>

Just remember that del is a statement, not a function or an operator. It does not evaluate to any return value.

Lists of Lists

Lists are a data type that can contain other values as items in the list. But these items can also be other lists. Let's say you have a list of groceries, a list of chores, and a list of your favorite pies. You can put all three of these lists into another list. Try typing this into the shell:

>>> groceries = ['eggs', 'milk', 'soup', 'apples', 'bread']
>>> chores = ['clean', 'mow the lawn', 'go grocery shopping']
>>> favoritePies = ['apple', 'frumbleberry']
>>> listOfLists = [groceries, chores, favoritePies]
>>> listOfLists
[['eggs', 'milk', 'soup', 'apples', 'bread'], ['clean', 'mow the lawn', 'go grocery shopping'], ['apple', 'frumbleberry']]
>>>

You could also type the following and get the same values for all four variables:

>>> listOfLists = [['eggs', 'milk', 'soup', 'apples', 'bread'], ['clean', 'mow the lawn', 'go grocery shopping'], ['apple', 'frumbleberry']]
>>> groceries = listOfLists[0]
>>> chores = listOfLists[1]
>>> favoritePies = listOfLists[2]
>>> groceries
['eggs', 'milk', 'soup', 'apples', 'bread']
>>> chores
['clean', 'mow the lawn', 'go grocery shopping']
>>> favoritePies
['apple', 'frumbleberry']
>>>

To get an item inside the list of lists, you would use two sets of square brackets like this: listOfLists[1][2] which would evaluate to the string 'go grocery shopping'. This is because listOfLists[1] evaluates to the list ['clean', 'mow the lawn', 'go grocery shopping'][2]. That finally evaluates to 'go grocery shopping'.

Here is another example of a list of lists, along with some of the indexes that point to the items in the list of lists named x. The red arrows point to indexes of the inner lists themselves. The image is also flipped on its side to make it easier to read:


Figure 9-1: The indexes of a list of lists.


Figure 9-1: The indexes of a list of lists.

Methods

Methods are just like functions, but they are always attached to a value. For example, all string values have a lower() method, which returns a copy of the string value in lowercase. You cannot just call lower() by itself and you do not pass a string argument to lower() by itself (as in lower('Hello')). You must attach the method call to a specific string value using a period.

The lower() and upper() String Methods

Try entering 'Hello world!'.lower() into the interactive shell to see an example of this method:

>>> 'Hello world'.lower()
'hello world!'
>>>

There is also an upper() method for strings, which changes all the characters in a string to uppercase. Try entering 'Hello world'.upper() into the shell:

>>> 'Hello world'.upper()
'HELLO WORLD! '
>>>

Because the upper() method returns a string, you can call a method on that string as well. Try typing 'Hello world!'.upper().lower() into the shell:

>>> 'Hello world'.upper().lower()
'hello world!'
>>>

'Hello world!'.upper() evaluates to the string 'HELLO WORLD!', and then we call that string's lower() method. This returns the string 'hello world!', which is the final value in the evaluation. The order is important. 'Hello world!'.lower().upper() is not the same as 'Hello world!'.upper().lower():

>>> 'Hello world'.lower().upper()
'HELLO WORLD!'
>>>

Remember, if a string is stored in a variable, you can call a string method on that variable. Look at this example:

>>> fizz = 'Hello world'
>>> fizz.upper()
'HELLO WORLD'
>>>

The reverse() and append() List Methods

The list data type also has methods. The reverse() method will reverse the order of the items in the list. Try entering spam = [1, 2, 3, 4, 5, 6, 'meow', 'woof'], and then spam.reverse() to reverse the list. Then enter spam to view the contents of the variable.

>>> spam = [1, 2, 3, 4, 5, 6, 'meow', 'woof']
>>> spam.reverse()
>>> spam
['woof', 'meow', 6, 5, 4, 3, 2, 1]
>>>

The most common list method you will use is append(). This method will add the value you pass as an argument to the end of the list. Try typing the following into the shell:

>>> eggs = []
>>> eggs.append('hovercraft')
>>> eggs
['hovercraft']
>>> eggs.append('eels')
>>> eggs
['hovercraft', 'eels']
>>> eggs.append(42)
>>> eggs
['hovercraft', 'eels', 42]
>>>

Though string and list data types have methods, integers do not happen to have any methods.

The Difference Between Methods and Functions

You may be wondering why Python has methods, since they seem to act just like functions. Some data types have methods. Methods are functions associated with values of that data type. For example, string methods are functions that can be called on any string. If you have the string value 'Hello', you could call the string method upper() like this: 'Hello'.upper(). Or if the string 'Hello' were stored in a variable named spam, it would look like this: spam.upper()

You cannot call string methods on values of other data types. For example, [1, 2, 'apple'].upper() would cause an error because [1, 2, 'apple'] is a list and upper() is a string method.

The values of data types that have methods are also called objects. Object-oriented programming is a bit advanced for this book, and you don't need to understand it to make games. Just understand that objects are another name for a values of data types that have methods. For example, all strings and lists are objects.

The split() List Method

Line 59 is a very long line of code, but it is really just a simple assignment statement. This line also uses the split() method, which is a method for the string data type (just like the lower() and upper() methods).

  1. words = 'ant baboon badger bat bear beaver camel cat clam cobra cougar coyote crow deer dog donkey duck eagle ferret fox frog goat goose hawk lion lizard llama mole monkey moose mouse mule newt otter owl panda parrot pigeon python rabbit ram rat raven rhino salmon seal shark sheep skunk sloth snake spider stork swan tiger toad trout turkey turtle weasel whale wolf wombat zebra'.split()

As you can see, this line is just one very long string, full of words separated by spaces. And at the end of the string, we call the split() method. The split() method changes this long string into a list, with each word making up a single list item. The "split" occurs wherever a space occurs in the string. The reason we do it this way, instead of just writing out the list, is that it is easier for us to type as one long string. If we created it as a list to begin with, we would have to type: ['ant', 'baboon', 'badger',... and so on, with quotes and commas for every single word.

For an example of how the split() string method works, try typing this into the shell:

>>> 'My very energetic mother just served us nine pies'.split()
['My', 'very', 'energetic', 'mother', 'just', 'served', 'us', 'nine', 'pies']
>>>

The result is a list of nine strings, one string for each of the words in the original string. The spaces are dropped from the items in the list. Once we've called split(), the words list will contain all the possible secret words that can be chosen by the computer for our Hangman game. You can also add your own words to the string, or remove any you don't want to be in the game. Just make sure that the words are separated by spaces.

How the Code Works

Starting on line 61, we define a new function called getRandomWord(), which has a single parameter named wordList. We will call this function when we want to pick a single secret word from a list of secret words.

  1. def getRandomWord(wordList):
  2.     # This function returns a random string from the passed list of strings.
  3.     wordIndex = random.randint(0, len(wordList) - 1)
  4.     return wordList[wordIndex]

The function getRandomWord() is passed a list of strings as the argument for the wordList parameter. On line 63, we will store a random index for this list in the wordIndex variable. We do this by calling randint() with two arguments. Remember that arguments in a function call are separated by commas, so the first argument is 0 and the second argument is len(wordList) - 1. The second argument is an expression that is first evaluated. len(wordList) will return the integer size of the list passed to getRandomWord(), and then we subtract one.

The reason we need the - 1 is because the indexes for lists start at 0, not 1. If we have a list of three items, the index of the first item is 0, the index of the second item is 1, the index of the third item is 2. The length of this list is 3, but the index 3 is after the last index. This is why we subtract 1 from the length.

For example, if we passed ['apple', 'orange', grape'] as an argument to getRandomWord(), then len(wordList) would return the integer 3 and the expression 3 - 1 would evaluate to the integer 2.

That means that wordIndex would contain the return value of randint(0, 2), which means wordIndex would equal 0, 1, or 2. On line 64, we would return the element in wordList at the integer index stored in wordIndex.

Let's pretend we did send ['apple', 'orange', grape'] as the argument to getRandomWord() and that randint(0, 2) returned the integer 2. That would mean that line 64 would become return wordList[2], which would evaluate to return 'grape'. This is how the getRandomWord() returns a random string in the wordList list. The following code entered into the interactive shell demonstrates this:

>>> wordIndex = 2
>>> print(wordIndex)
2
>>> print(['apple', 'orange', 'grape'][wordIndex])
grape
>>>

And remember, we can pass any list of strings we want to the getRandomWord() function, which is what makes it so useful for our Hangman game.

Displaying the Board to the Player

Next we need to create another function which will print the hangman board on the screen, along with how many letters the player has correctly (and incorrectly) guessed.

  1. def displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord):
  2.     print(HANGMANPICS[len(missedLetters)])
  3.     print()

This code defines a new function named displayBoard(). This function has four parameters. This function will implement the code for the "Show the board and blanks to the player" box in our flow chart. Here is what each parameter means:

The first print() function call will display the board. HANGMANPICS will be a list of strings for each possible board. HANGMANPICS[0] shows an empty gallows, HANGMANPICS[1] shows the head (this happens when the player misses one letter), HANGMANPICS[2] shows a head and body (this happens when the player misses two letters), and so on until HANGMANPICS[6] when the full hangman is shown and the player loses.

The number of letters in missedLetters will tell us how many incorrect guesses the player has made. We can call len(missedLetters) to find out this number. This number can also be used as the index to the HANGMANPICS list, which will allow us to print the correct board for the number of incorrect guesses. So, if missedLetters is 'aetr' then len('aetr') will return 4 and we will display the string HANGMANPICS[4]. This is what HANGMANPICS[len(missedLetters)] evaluates to. This line shows the correct hangman board to the player.

  1.     print('Missed letters:', end=' ')
  2.     for letter in missedLetters:
  3.         print(letter, end=' ')
  4.     print()

Line 71 is a new type of loop, called a for loop. A for loop is kind of like a while loop. Line 72 is the entire body of the for loop. The range() function is often used with for loops. I will explain both in the next two sections.

Remember that the keyword argument end=' ' uses only one = sign (like =), not two (like ==).

The range() and list() Functions

The range() function is easy to understand. You can call it with either one or two integer arguments. When called with one argument, range() will return a range object of integers from 0 up to (but not including) the argument. This range object can be converted to the more familiar list data type with the list() function. Try typing list(range(10)) into the shell:

>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>>

The list() function is very similar to the str() or int() functions. It just converts the object it is passed into a list. It's very easy to generate huge lists with the range() function. Try typing in list(range(10000)) into the shell:

>>> list(range(10000))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,...
      ...The text here has been skipped for brevity...
...9989, 9990, 9991, 9992, 9993, 9994, 9995, 9996, 9997, 9998, 9999]
>>>

The list is so huge, that it won't even all fit onto the screen. But we can save the list into the variable just like any other list by entering this:

>>> spam = list(range(10000))
>>>

If you pass two arguments to range(), the list of integers it returns is from the first argument up to (but not including) the second argument. Try typing list(range(10, 20)) into the shell:

>>> list(range(10, 20))
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
>>>

The range() is a very useful function, because we often use it in for loops (which are much like the while loops we have already seen).

for Loops

The for loop is very good at looping over a list of values. This is different from the while loop, which loops as long as a certain condition is true. A for statement begins with the for keyword, followed by a variable name, followed by the in keyword, followed by a sequence (such as a list or string) or a range object (returned by the range() function), and then a colon. Each time the program execution goes through the loop (that is, on each iteration through the loop) the variable in the for statement takes on the value of the next item in the list.

For example, you just learned that the range() function will return a list of integers. We will use this list as the for statement's list. In the shell, type for i in range(10): and press Enter. Nothing will happen, but the shell will indent the cursor and change the prompt from >>> to ... because it is waiting for you to type in the for-block. Type print(i) and press Enter. Then, to tell the interactive shell you are done typing in the for-block, press Enter again to enter a blank line. The shell will then execute your for statement and block:

>>> for i in range(10):
...     print(i)
...
0
1
2
3
4
5
6
7
8
9
>>>

Notice that with for loops, you do not need to convert the range object returned by the range() function into a list with list(). for loops do this for us automatically.

The for loop executes the code inside the for-block once for each item in the list. Each time it executes the code in the for-block, the variable i is assigned the next value of the next item in the list. If we used the for statement with the list [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] instead of range(10), it would have been the same:

>>> for i in [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]:
...     print(i)
...
0
1
2
3
4
5
6
7
8
9
>>>

The for statement automatically converts the range object returned by range() into a list, so there is no need to put something like list(range(10)) in the for statemet, just use range(10).

Try typing this into the shell: for thing in ['cats', 'pasta', 'programming', 'spam']: and press Enter, then type print('I really like ' + thing) and press Enter, and then press Enter again to tell the shell to end the for-block. The output should look like this:

>>> for thing in ['cats', 'pasta', 'programming', 'spam']:
...     print('I really like ' + thing)
...
I really like cats
I really like pasta
I really like programming
I really like spam
>>

And remember, because strings are also a sequence data type just like lists, you can use them in for statements as well. This example uses a single character from the string on each iteration:

>>> for i in 'Hello world!':
...     print(i)
...
H
e
l
l
o

w
o
r
l
d
!
>>>

A while Loop Equivalent of a for Loop

The for loop is very similar to the while loop, but when you only need to iterate over items in a list, using a for loop is much less code to type. You can make a while loop that acts the same way as a for loop by adding extra code:

>>> sequence = ['cats', 'pasta', 'programming', 'spam']
>>> index = 0
>>> while (index < len(sequence)):
...     thing = sequence[index]
...     print('I really like ' + thing)
...     index = index + 1
...
I really like cats
I really like pasta
I really like programming
I really like spam
>>>

But using the for statement automatically does all this extra code for us and makes programming easier since we have less to type. Our Hangman game will use for loops so you can see how useful they are in real games.

One more thing about for loops, is that the for statement has the in keyword in it. But when you use the in keyword in a for statement, Python does not treat it like the in operator you would use in something like 42 in [0, 42, 67]. The in keyword in for statements is just used to separate the variable and the list it gets its values from.

The rest of the displayBoard() function displays the missed letters and creates the string of the secret word with all the unguessed letters as blanks.

        print('Missed letters:', end=' ')
        for letter in missedLetters:
            print(letter, end=' ')
        print()

This for loop on line 71 will display all the missed guesses that the player has made. When you play Hangman on paper, you usually write down these letters off to the side so you know not to guess them again. On each iteration of the loop the value of letter will be each letter in missedLetters in turn. Remember that the end=' ' will replace the newline character that is printed after the string with a single space character.

If missedLetters was 'ajtw' then this for loop would display a j t w.

Slices and Slicing

If we want to get a shorter copy of some of the items in a list, we can use list slicing. Slicing creates a duplicate list out of some or all of the items in another list. In code, we can create a slice of a list by specifying two indexes (the beginning and end) and a colon. For example, type the following into the interactive shell:

>>> spam = ['apples', 'oranges', 'pears', 'bananas']
>>> eggs = spam[1:3]
>>> eggs
['oranges', 'pears']

The expression spam[0:2] evaluates to a list that contains all the items from index 0 up to (but not including) index 2 in spam. We store this smaller list in the variable eggs.

If you leave out the first index, Python will automatically think you want to specify index 0 for the first index:

>>> spam = ['apples', 'oranges', 'pears', 'bananas']
>>> spam[:3]
['apples', 'oranges', 'pears']

If you leave out the second index, Python will automatically think you want to specify the rest of the list:

>>> spam = ['apples', 'oranges', 'pears', 'bananas']
>>> spam[1:]
['oranges', 'pears', 'bananas']

Slicing is a simple way to get a subset of the items in a list. You can also use slices with strings in the same way you use them with lists. Each character in the string is like an item in the list. Try typing the following into the shell:

>>> myName = 'Zophie the Fat Cat'
>>> myName[4:12]
'ie the F'
>>> myName[:10]
'Zophie the'
>>> myName[7:]
'the Fat Cat'
>>>

Slices are used in the next part of the code we look at.

Displaying the Secret Word with Blanks

So by this point we have shown the player the hangman board and the missed letters. Now we want to print the secret word, except we want blank lines for the letters. We can use the _ character (called the underscore character) for this. But we should print the letters in the secret word that the player has guessed, and use _ characters for the letters the player has not guessed yet. We can first create a string with nothing but one underscore for each letter in the secret word. Then we can replace the blanks for each letter in correctLetters. So if the secret word was 'otter' then the blanked out string would be '_____' (five _ characters). If correctLetters was the string 'rt' then we would want to change the blanked string to '_tt_r'. Here is the code that does that:

  1.     blanks = '_' * len(secretWord)
  2.     for i in range(len(secretWord)): # replace blanks with correctly guessed letters
  3.         if secretWord[i] in correctLetters:
  4.             blanks = blanks[:i] + secretWord[i] + blanks[i+1:]
  5.     for letter in blanks: # show the secret word with spaces in between each letter

Line 75 creates the blanks variable full of _ underscores using string replication. Remember that the * operator can also be used on a string and an integer, so the expression 'hello' * 3 evaluates to 'hellohellohello'. This will make sure that blanks has the same number of underscores as secretWord has letters.

Then we use a for loop to go through each letter in secretWord and replace the underscore with the actual letter if it exists in correctLetters. Line 79 may look confusing. It seems that we are using the square brackets with the blanks and secretWord variables. But wait a second, blanks and secretWord are strings, not lists. And the len() function also only takes lists as parameters, not strings. But in Python, many of the things you can do to lists you can also do to strings such as replication, indexing, and slicing.

Replacing the Underscores with Correctly Guessed Letters

  1.     for i in range(len(secretWord)): # replace blanks with correctly guessed letters
  2.         if secretWord[i] in correctLetters:
  3.             blanks = blanks[:i] + secretWord[i] + blanks[i+1:]

Let's pretend the value of secretWord is 'otter' and the value in correctLetters is 'tr'. Then len(secretWord) will return 5. Then range(len(secretWord)) becomes range(5), which in turn returns the list [0, 1, 2, 3, 4].

Because the value of i will take on each value in [0, 1, 2, 3, 4], then the for loop code is equivalent to this:

if secretWord[0] in correctLetters:
blanks = blanks[:0] + secretWord[0] + blanks[1:]
if secretWord[1] in correctLetters:
blanks = blanks[:1] + secretWord[1] + blanks[2:]
if secretWord[2] in correctLetters:
blanks = blanks[:2] + secretWord[2] + blanks[3:]
if secretWord[3] in correctLetters:
blanks = blanks[:3] + secretWord[3] + blanks[4:]
if secretWord[4] in correctLetters:
blanks = blanks[:4] + secretWord[4] + blanks[5:]

(By the way, writing out the code like this is called loop unrolling.)

If you are confused as to what the value of something like secretWord[0] or blanks[3:] is, then look at this picture. It shows the value of the secretWord and blanks variables, and the index for each letter in the string.


Figure 9-2: The indexes of the blanks and secretWord strings.

If we replace the list slices and the list indexes with the values that they represent, the unrolled loop code would be the same as this:

if 'o' in 'tr': # False, blanks == '_____'
    blanks = '' + 'o' + '____' # This line is skipped.
if 't' in 'tr': # True, blanks == '_____'
    blanks = '_' + 't' + '___' # This line is executed.
if 't' in 'tr': # True, blanks == '_t___'
    blanks = '_t' + 't' + '__' # This line is executed.
if 'e' in 'tr': # False, blanks == '_tt__'
    blanks = '_tt' + 'e' + '_' # This line is skipped.
if 'r' in 'tr': # True, blanks == '_tt__'
    blanks = '_tt_' + 'r' + '' # This line is executed.
# blanks now has the value '_tt_r'

The above three code examples all do the same thing (at least, they do when secretWord is 'otter' and correctLetters is 'tr'. The first box is the actual code we have in our game. The second box shows code that does the same thing except without a for loop. The third box is the same as the second box, except we have evaluated many of the expressions in the second box.

The next few lines of code display the new value of blanks with spaces in between each letter.

  1.     for letter in blanks: # show the secret word with spaces in between each letter
  2.         print(letter, end=' ')
  3.     print()

This for loop will print out each character in the string blanks. Remember that by now, blanks may have some of its underscores replaced with the letters in secretWord. The end keyword argument in line 82's print() call makes the print() function put a space character at the end of the string instead of a newline character. This is the end of the displayBoard() function.

Get the Player's Guess

The getGuess() function we create next will be called whenever we want to let the player type in a letter to guess. The function returns the letter the player guessed as a string. Further, getGuess() will make sure that the player types a valid letter before returning from the function.

  1. def getGuess(alreadyGuessed):
  2.     # Returns the letter the player entered. This function makes sure the player entered a single letter, and not something else.

The getGuess() function has a string parameter called alreadyGuessed which should be passed a string that contains the letters the player has already guessed, and will ask the player to guess a single letter. This single letter will be the return value for this function.

  1.     while True:
  2.         print('Guess a letter.')
  3.         guess = input()
  4.         guess = guess.lower()

We will use a while loop because we want to keep asking the player for a letter until they enter text that is a single letter they have not guessed previously. Notice that the condition for the while loop is simply the Boolean value True. That means the only way execution will ever leave this loop is by executing a break statement (which leaves the loop) or a return statement (which leaves the entire function). Such a loop is called an infinite loop, because it will loop forever (unless it reaches a break statement).

The code inside the loop asks the player to enter a letter, which is stored in the variable guess. If the player entered a capitalized letter, it will be converted to lowercase on line 90.

elif ("Else If") Statements

Take a look at the following code:

if catName == 'Fuzzball':
    print('Your cat is fuzzy.')
else:
    print('Your cat is not very fuzzy at all.')

We've seen code like this before and it's rather simple. If the catName variable is equal to the string 'Fuzzball', then the if statement's condition is True and we tell the user that her cat is fuzzy. If catName is anything else, then we tell the user her cat is not fuzzy.

But what if we wanted something else besides "fuzzy" and "not fuzzy"? We could put another if and else statement inside the first else block like this:

if catName == 'Fuzzball':
    print('Your cat is fuzzy.')
else:
    if catName == 'Spots'
        print('Your cat is spotted.')
    else:
        print('Your cat is neither fuzzy nor spotted.')

But if we wanted more things, then the code starts to have a lot of indentation:

if catName == 'Fuzzball':
    print('Your cat is fuzzy.')
else:
    if catName == 'Spots'
        print('Your cat is spotted.')
    else:
        if catName == 'FattyKitty'
            print('Your cat is fat.')
        else:
            if catName == 'Puff'
                print('Your cat is puffy.')
            else:
                print('Your cat is neither fuzzy nor spotted nor fat nor puffy.')

Typing all those spaces means you have more chances of making a mistake with the indentation. So Python has the elif keyword. Using elif, the above code looks like this:

if catName == 'Fuzzball':
    print('Your cat is fuzzy.')
elif catName == 'Spots'
    print('Your cat is spotted.')
elif catName == 'FattyKitty'
    print('Your cat is fat.')
elif catName == 'Puff'
    print('Your cat is puffy.')
else:
    print('Your cat is neither fuzzy nor spotted nor fat nor puffy.')

If the condition for the if statement is False, then the program will check the condition for the first elif statement (which is catName == 'Spots'). If that condition is False, then the program will check the condition of the next elif statement. If all of the conditions for the if and elif statements are False, then the code in the else block executes.

But if one of the elif conditions are True, the elif-block code is executed and then execution jumps down to the first line past the else-block. So only one of the blocks in this if-elif-else statement will be executed. You can also leave off the else-block if you don't need one, and just have an if-else statement.

Making Sure the Player Entered a Valid Guess

  1.        if len(guess) != 1:
  2.            print('Please enter a single letter.')
  3.        elif guess in alreadyGuessed:
  4.            print('You have already guessed that letter. Choose again.')
  5.        elif guess not in 'abcdefghijklmnopqrstuvwxyz':
  6.            print('Please enter a LETTER.')
  7.        else:
  8.             return guess

The guess variable contains the text the player typed in for their letter guess. We need to make sure they typed in one and only one lowercase letter. If they didn't, we should loop back and ask them again. The if statement's condition checks that the text is one and only letter. If it is not, then we execute the if-block code, and then execution jumps down past the else-block. But since there is no more code after this if-elif-else statement, execution loops back to line 87.

If the condition for the if statement is False, we check the elif statement's condition on line 93. This condition is True if the letter exists inside the alreadyGuessed variable (remember, this is a string that has every letter the player has already guessed). If this condition is True, then we display the error message to the player, and jump down past the else-block. But then we would be at the end of the while-block, so execution jumps back up to line 87.

If the condition for the if statement and the elif statement are both False, then we check the second elif statement's condition on line 95. If the player typed in a number or a funny character (making guess have a value like '5' or '!'), then guess would not exist in the string 'abcdefghijklmnopqrstuvwxyz'. If this is the case, the elif statement's condition is True.

Figure 9-3 is an example of elif statements. Unless these three conditions are all False, the code will not return and the loop will keep asking for a letter. But when all three of the conditions are False, then the else-block's return statement will run and we will exit this loop and function.


Figure 9-3: The elif statement.

Asking the Player to Play Again

  1. def playAgain():
  2.     # This function returns True if the player wants to play again, otherwise it returns False.
  3.     print('Do you want to play again? (yes or no)')
  4.     return input().lower().startswith('y')

The playAgain() function has just a print() function call and a return statement. The return statement has an expression that looks complicated, but we can break it down. Once we evaluate this expression to a value, that value will be returned from this function.

The expression on line 103 doesn't have any operators, but it does have a function call and two method calls. The function call is input() and the method calls are lower() and startswith('y'). Remember that method calls are function calls that are attached by a period to the value on their left. lower() is attached to the return value of input().

input() returns a string of the text that the user typed in. Here's a step by step look at how Python evaluates this expression if the user types in YES.

input().lower().startswith('y')
    A downward arrow
'YES'.lower().startswith('y')
    A downward arrow
'yes'.startswith('y')
    A downward arrow
True

The point of the playAgain() function is to let the player type in yes or no to tell our program if they want to play another round of Hangman. If the player types in YES, then the return value of input() is the string 'YES'. And 'YES'.lower() returns the lowercase version of the attached string. So the return value of 'YES'.lower() is 'yes'.

But there's the second method call, startswith('y'). This function returns True if the associated string begins with the string parameter between the parentheses, and False if it doesn't. The return value of 'yes'.startswith('y') is True.

Now we have evaluated this expression! We can see that what this does is let the player type in a response, we lowercase the response, check if it begins with the letter 'y' or 'Y', and then return True if it does and False if it doesn't. Whew!

On a side note, there is also a endswith(someString) string method that will return True if the string ends with the string in someString and False if it doesn't. endswith() is sort of like the opposite of startswith().

Review of the Functions We Defined

That's all the functions we are creating for this game!

We'll now start the code for the main part of the game, which will call the above functions as needed. As a refresher, look back at our flow chart in Figure 9-4.


Figure 9-4: The complete flow chart of Hangman.

The Main Code for Hangman

We need to write code that does everything in this flow chart, and does it in the correct order. The main part of the code starts at line 106. Everything previous was just function definitions and a very large variable assignment for HANGMANPICS.

Setting Up the Variables

  1. print('H A N G M A N')
  2. missedLetters = ''
  3. correctLetters = ''
  4. secretWord = getRandomWord(words)
  5. gameIsDone = False

Line 106 is the first actual line that executes in our game. We start by assigning a blank string for missedLetters and correctLetters, because the player has not guessed any missed or correct letters yet. Then we call getRandomWord(words), where words is a variable with the huge list of possible secret words we assigned on line 59. The return value of getRandomWord(words) is one of these words, and we save it to the secretWord variable. Then we also set a variable named gameIsDone to False. We will set gameIsDone to True when we want to signal that the game is over and the program should ask the player if they want to play again.

Setting the values of these variables is what we do before the player starts guessing letters.

Displaying the Board to the Player

  1. while True:
  2.     displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)

The while loop's condition is always True, which means we will always loop forever until a break statement is encountered. We will execute a break statement when the game is over (either because the player won or the player lost).

Line 113 calls our displayBoard() function, passing it the list of hangman ASCII art pictures and the three variables we set on lines 107, 108, and 109. The execution moves to the start of displayBoard() at line 66. Based on how many letters the player has correctly guessed and missed, this function displays the appropriate hangman board to the player.

Letting the Player Enter Their Guess

  1.     # Let the player type in a letter.
  2.     guess = getGuess(missedLetters + correctLetters)

If you look at our flow chart, you see only one arrow going from the "Show the board and the blanks to the player." box to the "Ask a player to guess a letter." box. Since we have already written a function to get the guess from the player, let's call that function. Remember that the function needs all the letters in missedLetters and correctLetters combined, so we will pass as an argument a string that is a concatenation of both of those strings. This argument is needed by getGuess() because the function has code to check if the player types in a letter that they have already guessed.

Checking if the Letter is in the Secret Word

  1.     if guess in secretWord:
  2.         correctLetters = correctLetters + guess

Now let's see if the single letter in the guess string exists in secretWord. If it does exist, then we should concatenate the letter in guess to the correctLetters string. Next we can check if we have guessed all of the letters and won.

Checking if the Player has Won

  1.         # Check if the player has won
  2.         foundAllLetters = True
  3.         for i in range(len(secretWord)):
  4.             if secretWord[i] not in correctLetters:
  5.                 foundAllLetters = False
  6.                 break

How do we know if the player has guessed every single letter in the secret word? Well, correctLetters has each letter that the player correctly guessed and secretWord is the secret word itself. We can't just check if correctLetters == secretWord because consider this situation: if secretWord was the string 'otter' and correctLetters was the string 'orte', then correctLetters == secretWord would be False even though the player has guessed each letter in the secret word.

The player simply guessed the letters out of order and they still win, but our program would incorrectly think the player hasn't won yet. Even if they did guess the letters in order, correctLetters would be the string 'oter' because the player can't guess the letter t more than once. The expression 'otter' == 'oter' would evaluate to False even though the player guessed all the letters.

The only way we can be sure the player won is to go through each letter in secretWord and see if it exists in correctLetters. If, and only if, every single letter in secretWord exists in correctLetters will the player have won.

Note that this is different than checking if every letter in correctLetters is in secretWord. If correctLetters was the string 'ot' and secretWord was 'otter', it would be true that every letter in 'ot' is in 'otter', but that doesn't mean the player has guessed the secret word and won.

So how can we do this? We can loop through each letter in secretWord and if we find a letter that does not exist in correctLetters, we know that the player has not guessed all the letters. This is why we create a new variable named foundAllLetters and set it to the Boolean value True. We start out assuming that we have found all the letters, but will change foundAllLetters to False when we find a letter in secretWord that is not in correctLetters.

The for loop will go through the numbers 0 up to (but not including) the length of the word. Remember that range(5) will evaluate to the list [0, 1, 2, 3, 4]. So on line 123, the program executes all the code inside the for-block five times. The first time it executes with the variable i set to 0, the second time set to 1, then 2, then 3, then finally 4.

We use range(len(secretWord)) so that i can be used to access each letter in the secret word. So if the first letter in secretWord (which is located at secretWord[0]) is not in correctLetters, we know we can set foundAllLetters to False. Also, because we don't have to check the rest of the letters in secretWord, we can just break out of this loop. Otherwise, we loop back to line 123 and check the next letter.

If foundAllLetters manages to stay set to True, then it will keep the original True value we gave it. Either way, the value in foundAllLetters is accurate by the time we get past this for loop and run line 127.

  1.         if foundAllLetters:
  2.             print('Yes! The secret word is "' + secretWord + '"! You have won!')
  3.             gameIsDone = True

This is a simple check to see if we found all the letters. If we have found every letter in the secret word, we should tell the player that they have won. We will also set the gameIsDone variable to True. We will check this variable to see if we should let the player guess again or if the player is done guessing.

When the Player Guesses Incorrectly

  1.     else:

This is the start of the else-block. Remember, the code in this block will execute if the condition was False. But which condition? To find out, point your finger at the start of the else keyword and move it straight up. You will see that the else keyword's indentation is the same as the if keyword's indentation on line 118. So if the condition on line 118 was False, then we will run the code in this else-block. Otherwise, we skip down past the else-block to line 140.

  1.         missedLetters = missedLetters + guess

Because the player's guessed letter was wrong, we will add it to the missedLetters string. This is like what we did on line 119 when the player guessed correctly.

  1.         # Check if player has guessed too many times and lost
  2.         if len(missedLetters) == len(HANGMANPICS) - 1:
  3.             displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)
  4.             print('You have run out of guesses!\nAfter ' + str(len(missedLetters)) + ' missed guesses and ' + str(len(correctLetters)) + ' correct guesses, the word was "' + secretWord + '"')
  5.             gameIsDone = True

Think about how we know when the player has guessed too many times. When you play Hangman on paper, this is when the drawing of the hangman is finished. We draw the hangman on the screen with print() calls, based on how many letters are in missedLetters. Remember that each time the player guesses wrong, we add (or as a programmer would say, concatenate) the wrong letter to the string in missedLetters. So the length of missedLetters (or, in code, len(missedLetters)) can tell us the number of wrong guesses.

At what point does the player run out of guesses and lose? Well, the HANGMANPICS list has 7 pictures (really, they are ASCII art strings). So when len(missedLetters) equals 6, we know the player has lost because the hangman picture will be finished. (Remember that HANGMANPICS[0] is the first item in the list, and HANGMANPICS[6] is the last one. This is because the index of a list with 7 items goes from 0 to 6, not 1 to 7.)

So why do we have len(missedLetters) == len(HANGMANPICS) - 1 as the condition on line 134, instead of len(missedLetters) == 6? Pretend that we add another string to the HANGMANPICS list (maybe a picture of the full hangman with a tail, or a third mutant arm). Then the last picture in the list would be at HANGMANPICS[7]. So not only would we have to change the HANGMANPICS list with a new string, but we would also have to remember to change line 134 to len(missedLetters) == 7. This might not be a big deal for a small program like Hangman, but when you start writing larger programs you may have to change several different lines of code all over your program just to make a single change in the program's behavior. This way, if we want to make the game harder or easier, we just have to add or remove ASCII art strings to HANGMANPICS and change nothing else.

A second reason we user len(HANGMANPICS) - 1 is so that when we read the code in this program later, we know why this program behaves the way it does. If you wrote len(missedLetters) == 6 and then looked at the code two weeks later, you may wonder what is so special about the number 6. You may have forgotten that 6 is the last index in the HANGMANPICS list. Of course, you could write a comment to remind yourself, like:

if len(missedLetters) == 6: # 6 is the last index in the HANGMANPICS list

But it is easier to just use len(HANGMANPICS) - 1 instead.

So, when the length of the missedLetters string is equal to len(HANGMANPICS) - 1, we know the player has run out of guesses and has lost the game. We print a long string telling the user what the secret word was, and then set the gameIsDone value to the Boolean value True. This is how we will tell ourselves that the game is done and we should start over.

Remember that when we have \n in a string, that represents the newline character. That is how the one print() call on line 136 displays several lines of text.

  1.     # Ask the player if they want to play again (but only if the game is done).
  2.     if gameIsDone:
  3.         if playAgain():
  4.             missedLetters = ''
  5.             correctLetters = ''
  6.             gameIsDone = False
  7.             secretWord = getRandomWord(words)

If the player won or lost after guessing their letter, then our code would have set the gameIsDone variable to True. If this is the case, we should ask the player if they want to play again. We already wrote the playAgain() function to handle getting a yes or no from the player. This function returns a Boolean value of True if the player wants to play another game of Hangman, and False if they've had enough.

If the player does want to play again, we will reset the values in missedLetters and correctLetters to blank strings, set gameIsDone to False, and then choose a new secret word by calling getRandomWord() again, passing it the list of possible secret words.

This way, when we loop back to the beginning of the loop (on line 112) the board will be back to the start (remember we decide which hangman picture to show based on the length of missedLetters, which we just set as the blank string) and the game will be just as the first time we entered the loop. The only difference is we will have a new secret word, because we programmed getRandomWord() to return a randomly chosen word each time we call it.

There is a small chance that the new secret word will be the same as the old secret word, but this is just a coincidence. Let's say you flipped a coin and it came up heads, and then you flipped the coin again and it also came up heads. Both coin flips were random, it was just a coincidence that they came up the same both times. Accordingly, you may get the same word return from getRandomWord() twice in a row, but this is just a coincidence.

  1.         else:
  2.             break

If the player typed in 'no' when asked if they wanted to play again, then they return value of the call to the playAgain() function would be False and the else-block would have executed. This else-block only has one line, a break statement. This causes the execution to jump to the end of the loop that was started on line 112. But because there is no more code after the loop, the program terminates.

Making New Changes to the Hangman Program

This program was much bigger than the Dragon Realm program, but this program is also more sophisticated. It really helps to make a flow chart or small sketch to remember how you want everything to work. Take a look at the flow chart a few pages back in Figure 9-4 and try to find the lines of code that represent each block.

Let's look at some ways we can improve our Hangman game.

After you have played Hangman a few times, you might think that six guesses aren't enough to get many of the words. We can easily give the player more guesses by adding more multi-line strings to the HANGMANPICS list. It's easy, just change the ] square bracket on line 58 to a ,''' comma and three quotes (see line 57 below). Then add the following:

  1. ==========''', '''
  2.   +----+
  3.   |    |
  4.  [O    |
  5.  /|\   |
  6.  / \   |
  7.        |
  8. ==========''', '''
  9.   +----+
  10.   |    |
  11.  [O]   |
  12.  /|\   |
  13.  / \   |
  14.        |
  15. ==========''']

We have added two new multi-line strings to the HANGMANPICS list, one with the hangman's left ear drawn, and the other with both ears drawn. Because our program will tell the player they have lost when the number of guesses is the same as the number of strings in HANGMANPICS (minus one), this is the only change we need to make.

We can also change the list of words by changing the words on line 59. Instead of animals, we could have colors:

  1. words = 'red orange yellow green blue indigo violet white black brown'.split()

Or shapes:

  1. words = 'square triangle rectangle circle ellipse rhombus trapazoid chevron pentagon hexagon septagon octogon'.split()

Or fruits:

  1. words = 'apple orange lemon lime pear watermelon grape grapefruit cherry banana cantalope mango strawberry tomato'.split()

Dictionaries

With some modification, we can change our code so that our Hangman game can use all of these words as separate sets. We can tell the player which set the secret word is from (like "animal", "color", "shape", or "fruit"). This way, the player isn't guessing animals all the time.

To make this change, we will introduce a new data type called a dictionary. A dictionary is a collection of many values much like a list is, but instead of accessing the items in the dictionary with an integer index, you access them with an index (for dictionaries, the indexes are called keys) of any data type (but most often strings).

Try typing the following into the shell:

>>> stuff = {'hello':'Hello there, how are you?', 'chat':'How is the weather?', 'goodbye':'It was nice talking to you!'}
>>>

Those are curly braces { and }. On the keyboard they are on the same key as the square braces [ and ]. We use curly braces to type out a dictionary value in Python. The values in between them are key-value pairs. The keys are the things on the left of the colon and the values are on the right of the colon. You can access the values (which are like items in lists) in the dictionary by using the key (which are like indexes in lists). Try typing into the shell stuff['hello'] and stuff['chat'] and stuff['goodbye']:

>>> stuff['hello']
'Hello there, how are you?'
>>> stuff['chat']
'How is the weather?'
>>> stuff['goodbye']
'It was nice talking to you!'
>>>

Getting the Size of Dictionaries with len()

You see, instead of putting an integer index in between the square brackets, you put a string key. This will evaluate to the value for that key. You can get the size (that is, how many key-value pairs in the dictionary) with the len() function. Try typing len(stuff) into the shell:

>>> len(stuff)
3
>>>

The list version of this dictionary would have only the values, and look something like this:

listStuff = ['Hello there, how are you?', 'How is the weather?', 'It was nice talking to you!']

The list doesn't have any keys, like 'hello' and 'chat' and 'goodbye' in the dictionary. We have to use integer indexes 0, 1, and 2.

The Difference Between Dictionaries and Lists

Dictionaries are different from lists because they are unordered. The first item in a list named listStuff would be listStuff[0]. But there is no "first" item in a dictionary, because dictionaries do not have any sort of order. Try typing this into the shell:

>>> favorites1 = {'fruit':'apples', 'number':42, 'animal':'cats'}
>>> favorites2 = {'animal':'cats', 'number':42, 'fruit':'apples'}
>>> favorites1 == favorites2
True
>>>

As you can see, the expression favorites1 == favorites2 evaluates to True because dictionaries are unordered, and they are considered to be the same if they have the same key-value pairs in them. Lists are ordered, so a list with the same values in them but in a different order are not the same. Try typing this into the shell:

>>> listFavs1 = ['apples', 'cats', 42]
>>> listFavs2 = ['cats', 42, 'apples']
>>> listFavs1 == listFavs2
False
>>>

As you can see, the two lists listFavs1 and listFavs2 are not considered to be the same because order matters in lists.

You can also use integers as the keys for dictionaries. Dictionaries can have keys of any data type, not just strings. But remember, because 0 and '0' are different values, they will be different keys. Try typing this into the shell:

>>> myDict = {'0':'a string', 0:'an integer'}
>>> myDict[0]
'an integer'
>>> myDict['0']
'a string'
>>>

You might think that using a for loop is hard with dictionaries because they do not have integer indexes. But actually, it's easy. Try typing the following into the shell. (Here's a hint, in IDLE, you do not have to type spaces to start a new block. IDLE does it for you. To end the block, just insert a blank line by just hitting the Enter key. Or you could start a new file, type in this code, and then press F5 to run the program.)

>>> favorites = {'fruit':'apples', 'animal':'cats', 'number':42}
>>> for i in favorites:
...     print(i)

fruit
number
animal
>>> for i in favorites:
...     print(favorites[i])

apples
42
cats
>>>

As you can see, if you just use a dictionary in a for loop, the variable i will take on the values of the dictionary's keys, not its values. But if you have the dictionary and the key, you can get the value as we do above with favorites[i]. But remember that because dictionaries are unordered, you cannot predict which order the for loop will execute in. Above, we typed the 'animal' key as coming before the 'number' key, but the for loop printed out 'number' before 'animal'.

Dictionaries also have two useful methods, keys() and values(). These will return values of a type called dict_keys and dict_values, respectively. Those data types are beyond the scope of this book, but you can easily convert them to lists with the list() function (just like str() converts a value to a string value.) Then you will have an ordered list of the key values and the value values in the dictionary value. Try typing the following into the shell:

>>> favorites = {'fruit':'apples', 'animal':'cats', 'number':42}
>>> list(favorites.keys())
['fruit', 'number', 'animal']
>>> list(favorites.values())
['apples', 42, 'cats']
>>>

Using these methods to get a list of the keys and values that are in a dictionary can be very helpful. Do not forget to convert the return value of dict_keys and dict_keys with the dict_keys function first, otherwise you may get errors in your program.

Sets of Words for Hangman

We will make changes to our original Hangman program. These changes can be downloaded from http://inventwithpython.com/hangman2.py

So how can we use dictionaries in our game? First, let's change the list words into a dictionary whose keys are strings and values are lists of strings. (Remember that the string method split() evaluates to a list.

  1. words = {'Colors':'red orange yellow green blue indigo violet white black brown'.split(),
  2. 'Shapes':'square triangle rectangle circle ellipse rhombus trapazoid chevron pentagon hexagon septagon octogon'.split(),
  3. 'Fruits':'apple orange lemon lime pear watermelon grape grapefruit cherry banana cantalope mango strawberry tomato'.split(),
  4. 'Animals':'bat bear beaver cat cougar crab deer dog donkey duck eagle fish frog goat leech lion lizard monkey moose mouse otter owl panda python rabbit rat shark sheep skunk squid tiger turkey turtle weasel whale wolf wombat zebra'.split()}

This code is put across multiple lines in the file, even though the Python interpreter thinks of it as just one "line of code." (The line of code doesn't end until the final } curly brace.)

The random.choice() Function

Now we will have to change our getRandomWord() function so that it chooses a random word from a dictionary of lists of strings, instead of from a list of strings. Here is what the function originally looked like:

  1. def getRandomWord(wordList):
  2.     # This function returns a random string from the passed list of strings.
  3.     wordIndex = random.randint(0, len(wordList) - 1)
  4.     return wordList[wordIndex]

Change the code in this function so that it looks like this:

  1. def getRandomWord(wordDict):
  2.     # This function returns a random string from the passed dictionary of lists of strings, and the key also.
  3.     # First, randomly select a key from the dictionary:
  4.     wordKey = random.choice(list(wordDict.keys()))
  5.     # Second, randomly select a word from the key's list in the dictionary:
  6.     wordIndex = random.randint(0, len(wordDict[wordKey]) - 1)
  7.     return [wordDict[wordKey][wordIndex], wordKey]

Line 61 just changes the name of the parameter to something a little more descriptive. Now instead of choosing a random word from a list of strings, first we choose a random key from the dictionary and then we choose a random word from the key's list of strings. Line 65 calls a new function in the random module named choice(). The choice() function has one parameter, a list. The return value of choice() is an item randomly selected from this list each time it is called.

Remember that randint(a, b) will return a random integer between (and including) the two integers a and b and choice(a) returns a random item from the list a. Look at these two lines of code, and figure out why they do the exact same thing:

random.randint(0, 9)
random.choice(list(range(0, 10)))

Line 64 (line 70 in the new code) has also been changed. Now instead of returning the string wordList[wordIndex], we are returning a list with two items. The first item is wordDict[wordKey][wordIndex]. The second item is wordKey. We return a list because we actually want the getRandomWord() to return two values, so putting those two values in a list and returning the list is the easiest way to do this.

Evaluating a Dictionary of Lists

wordDict[wordKey][wordIndex] may look kind of complicated, but it is just an expression you can evaluate one step at a time like anything else. First, imagine that wordKey had the value 'Fruits' (which was chosen on line 65) and wordIndex has the value 5 (chosen on line 68). Here is how wordDict[wordKey][wordIndex] would evaluate:

wordDict[wordKey][wordIndex]
    A downward arrow
wordDict['Fruits'][5]
    A downward arrow
['apple', 'orange', 'lemon', 'lime', 'pear', 'watermelon', 'grape', 'grapefruit', 'cherry', 'banana', 'cantalope', 'mango', 'strawberry', 'tomato'][5]
    A downward arrow
'watermelon'

In the above case, the item in the list this function returns would be the string 'watermelon'. (Remember that indexes start at 0, so [5] refers to the 6th item in the list.)

There are just three more changes to make to our program. The first two are on the lines that we call the getRandomWord() function. The function is called on lines 109 and 145 in the original program:

  1.             correctLetters = ''
  2.             secretWord = getRandomWord(words)
  3.             gameIsDone = False

...

  1.             gameIsDone = False
  2.             secretWord = getRandomWord(words)
  3.         else:

Because the getRandomWord() function now returns a list of two items instead of a string, secretWord will be assigned a list, not a string. We would then have to change the code as follows:

  1. correctLetters = ''
  2. secretWord = getRandomWord(words)
  3. secretKey = secretWord[1]
  4. secretWord = secretWord[0]
  5. gameIsDone = False

...

  1. gameIsDone = False
  2. secretWord = getRandomWord(words)
  3. secretKey = secretWord[1]
  4. secretWord = secretWord[0]
  5. else:

With the above changes, secretWord is first a list of two items. Then we add a new variable named secretKey and set it to the second item in secretWord. Then we set secretWord itself to the first item in the secretWord list. That means that secretWord will then be a string.

Multiple Assignment

But there is an easier way by doing a little trick with assignment statements. Try typing the following into the shell:

>>> a, b, c = ['apples', 'cats', 42]
>>> a
'apples'
>>> b
'cats'
>>> c
42
>>>

The trick is to put the same number of variables (delimited by commas) on the left side of the = sign as are in the list on the right side of the = sign. Python will automatically assign the first item's value in the list to the first variable, the second item's value to the second variable, and so on. But if you do not have the same number of variables on the left side as there are items in the list on the right side, the Python interpreter will give you an error.

>>> a, b, c, d = ['apples', 'cats', 42]

Traceback (most recent call last):
  File "<pyshell#8>", line 1, in <module>
    a, b, c, d = ['apples', 'cats', 42, 10, 'hello']
ValueError: too many values to unpack

>>> a, b, c, d = ['apples', 'cats']

Traceback (most recent call last):
  File "<pyshell#9>", line 1, in <module>
    a, b, c = ['apples', 'cats']
ValueError: need more than 2 values to unpack
>>>

So we should change our code in Hangman to use this trick, which will mean our program uses fewer lines of code.

  1. correctLetters = ''
  2. secretWord, secretKey = getRandomWord(words)
  3. gameIsDone = False

...

  1. gameIsDone = False
  2. secretWord, secretKey = getRandomWord(words)
  3. else:

Printing the Word Category for the Player

The last change we will make is to add a simple print() call to tell the player which set of words they are trying to guess. This way, when the player plays the game they will know if the secret word is an animal, color, shape, or fruit. Add this line of code after line 112. Here is the original code:

  1. while True:
  2.     displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)

Add the line so your program looks like this:

  1. while True:
  2.     print('The secret word is in the set: ' + secretKey)
  3.     displayBoard(HANGMANPICS, missedLetters, correctLetters, secretWord)

Now we are done with our changes. Instead of just a single list of words, the secret word will be chosen from many different lists of words. We will also tell the player which set of words the secret word is from. Try playing this new version. You can easily change the words dictionary on line 59 to include more sets of words.

Summary

We're done with Hangman. This has been a long chapter, and several new concepts have been introduced. But Hangman has been our most advanced game yet. As your games get more and more complex, it'll be a good idea to sketch out a flow chart on paper of what happens in your program.

Methods are just like functions, except that are associated with values. Methods return values just like functions return values.

for loops iterate over the items in a list. The range() function is often used with for loops because it is an easy way to create lists of sequential numbers.

Else-if statements (which use the elif keyword) will execute their block if their condition is True and the previous if and elif conditions are False

Dictionaries are very similar to lists except that they can use any value for an index. The indexes in dictionaries are called keys. Keys can be strings, integers, or any value of any data type.

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