To get practice debugging programs, download the programs which each have a simple typo bug in them. For Appendix D of "Invent with Python" for a list of common error messages and what they mean, and read Chapter 7 of "Invent with Python" to learn how to use the debugger software that comes with IDLE.
You don't need to use the debugger to fix these programs, but it makes debugging much easier.
Download buggy Memory Puzzle programs.
memorypuzzle_buggy1.py - Graphics are messed up.
memorypuzzle_buggy2.py - IndexError: list index out of range
memorypuzzle_buggy3.py - Box highlight lags
memorypuzzle_buggy4.py - icons don't show up
memorypuzzle_buggy5.py - NameError: global name 'getRandomizedBoard' is not defined
memorypuzzle_buggy6.py - Box hide/reveal animation is very choppy.
memorypuzzle_buggy7.py - No gaps are showing up on the board.
memorypuzzle_buggy8.py - TypeError: 'NoneType' object is not iterable
Download buggy Slide Puzzle programs.
slidepuzzle_buggy1.py - Clicking reset crashes the game: "NameError: global name 'resetAnimation' is not defined"
slidepuzzle_buggy2.py - SyntaxError: EOL while scanning string literal
slidepuzzle_buggy3.py - Sliding down causes the tile to move down-right.
slidepuzzle_buggy4.py - Clicking Solve twice causes it to make several extra moves the second time.
slidepuzzle_buggy5.py - Game won't start: "pygame.error: font not initialized"
slidepuzzle_buggy6.py - SyntaxError: invalid syntax
slidepuzzle_buggy7.py - Clicking "New Game" causes "IndexError: string index out of range"
slidepuzzle_buggy8.py - Puzzle starts off with tiles shifted off by 1 space, and there are two blank spots.
Download buggy Simulate programs.
simulate_buggy1.py - Game crashes for no reason - "NameError: global name 'BRIGHTYELOW' is not defined"
simulate_buggy2.py - Blue button overlaps the yellow button.
simulate_buggy3.py - Pressing the "W" key doesn't work.
simulate_buggy4.py - Game crashes - "NameError: global name 'BEEP4' is not defined"
simulate_buggy5.py - Window appears too tall.
simulate_buggy6.py - Yellow button doesn't flash.
simulate_buggy7.py - Buttons don't flash.
simulate_buggy8.py - Game doesn't run - "IndentationError: unindent does not match any outer indentation level"
Download buggy Wormy programs.
wormy_buggy1.py - Worm sometimes does not appear on the board, and "Game Over" appears a second or two later.
wormy_buggy2.py - Worm keeps growing.
wormy_buggy3.py - Pressing down makes the worm go up.
wormy_buggy4.py - Worm can go off the left and right edges.
wormy_buggy5.py - Program hangs with a black screen when it first starts.
wormy_buggy6.py - NameError: global name 'DOWN' is not defined
wormy_buggy7.py - An invisible vertical wall near the middle causes the player to game over.
wormy_buggy8.py - Player can't change direction, and pressing the left arrow key causes a game over.
Download buggy Tetromino programs.
tetromino_buggy1.py - Music keeps going after Game Over
tetromino_buggy2.py - Game crashes in the middle for no reason - "IndexError: string index out of range"
tetromino_buggy3.py - "Press a key to play." text isn't in the center.
tetromino_buggy4.py - Game doesn't run. "NameError: name 'Z_SHAPE_TEMPLATE' is not defined"
tetromino_buggy5.py - Game crashes when a piece lands ("IndexError: list assignment index out of range"), or pieces change shape after landing.
tetromino_buggy6.py - Game crashes when a piece lands ("IndexError: list index out of range")
tetromino_buggy7.py - Complete lines won't clear.
tetromino_buggy8.py - Game freezes as soon as the player makes a complete line.
Download buggy Squirrel Eat Squirrel programs.
squirrel_buggy1.py - Game doesn't run - "KeyError: 'widht'"
squirrel_buggy2.py - Game never resets after the first game over.
squirrel_buggy3.py - First hit causes two damage, and then the player doesn't take damage afterwards.
squirrel_buggy4.py - Squirrel disappears after moving down.
squirrel_buggy5.py - Game doesn't run - "NameError: global name 'L_SQUIR_IMG' is not defined"
squirrel_buggy6.py - Game doesn't run - "TypeError: 'dict' object cannot be interpreted as an integer"
squirrel_buggy7.py - No squirrels show up.
squirrel_buggy8.py - When you win the game, "(Press "r" to restart.)" text doesn't appear in the center.
Download buggy Star Pusher programs.
starpusher_buggy1.py - Error when you first try to move: "TypeError: makeMove() takes exactly 2 positional arguments (3 given)"
starpusher_buggy2.py - Crashes when you solve a level: "KeyError: 'solve'"
starpusher_buggy3.py - Level is solved as soon as you make your first move.
starpusher_buggy4.py - Background is black on the start screen.
starpusher_buggy5.py - Game crashes at start of first level: "AssertionError: Level 1 (around line 35) in starPusherLevels.txt is missing a "@" or "+" to mark the start point." (But the map file is fine.)
starpusher_buggy6.py - Game crashes at start of the first level: "IndexError: list index out of range"
starpusher_buggy7.py - Game crashes at start of the first level: "AttributeError: event member not defined"
starpusher_buggy8.py - Map appears super skinny.
Download buggy Flippy programs.
flippy_buggy1.py - Black bar appears at the bottom of the screen.
flippy_buggy2.py - Game crashes on computer's turn - "TypeError: 'NoneType' object is not iterable"
flippy_buggy3.py - Board appears on right side of the screen.
flippy_buggy4.py - Computer wins at the start of the game with several pieces on the board.
flippy_buggy5.py - Game crashes on player's move - "TypeError: 'bool' object is not subscriptable"
flippy_buggy6.py - Game instantly ends as a tie.
flippy_buggy7.py - Game instantly ends as a tie.
flippy_buggy8.py - Player always goes first.
Download buggy Ink Spill programs.
inkspill_buggy1.py - Logo doesn't appear in the upper right
inkspill_buggy2.py - Can't select small board on settings page.
inkspill_buggy3.py - Player wins after first move.
inkspill_buggy4.py - Game doesn't run - "IndexError: list index out of range"
inkspill_buggy5.py - Game doesn't run - "NameError: name 'random' is not defined"
inkspill_buggy6.py - First move is always red, and then the player can't make any more moves.
inkspill_buggy7.py - Game is just a black screen.
inkspill_buggy8.py - Background is black.
Download buggy Four in a Row programs.
fourinarow_buggy1.py - Game won't run - "IndexError: list index out of range"
fourinarow_buggy2.py - Game won't run - "NameError: global name 'COMPUTER' is not defined"
fourinarow_buggy3.py - Game won't run - TypeError: 'NoneType' object is not iterable
fourinarow_buggy4.py - Computer will never move on the rightmost column. fourinarow_buggy5.py - If player's first move is not over the board, then the game crashes: "UnboundLocalError: local variable 'column' referenced before assignment"
fourinarow_buggy6.py - Game won't run - "IndexError: list index out of range"
fourinarow_buggy7.py - When dropping a token on a tall stack, the token appears to drop past the top token on the stack.
fourinarow_buggy8.py - Computer's token seems to fly off the screen, and then the program hangs.
Download buggy Gemgem programs.
gemgem_buggy1.py - Game doesn't run, and doesn't display any error message.
gemgem_buggy2.py - Game crashes at the start. "TypeError: drawBoard() takes exactly 1 positional argument (0 given)"
gemgem_buggy3.py - Game won't run - "pygame.error: Couldn't open gem8.png"
gemgem_buggy4.py - Game won't run - "TypeError: list indices must be integers, not str"
gemgem_buggy5.py - Matching gems gives a negative score, and moving a gem to make a match in a horizontal line doesn't cause two of the gems to disappear
gemgem_buggy6.py - First match causes other gems to disappear.
gemgem_buggy7.py - Board has missing rows of gems.
gemgem_buggy8.py - Game doesn't run - "NameError: global name 'BOARDRECTS' is not defined"