Quia - Class Page - Debugging Strategies Lesson Plan Answer Key

📚 Main Learning Objective:

Students will evaluate error messages to systematically resolve syntax and logic errors in Python code.

Lots of Hurdles

1 Error

Error #1 Line 1

⚠️ SYNTAX ERROR: Missing Function Definition

Error Message: NameError: name 'turn_right' is not defined

What's Wrong: The turn_right() function is called in jump_hurdle() but is never defined in the starter code.

✅ How to Fix:

Add the turn_right() function definition before it is used:

def turn_right():
    turn_left()
    turn_left()
    turn_left()
                    

Teaching Tip: Emphasize that functions must be defined before they are called. This is a common error for beginning programmers.

Big Tower

3 Errors

Error #1 Line 6

⚠️ LOGIC ERROR: Incorrect Condition

What's Wrong: The condition while facing_north(): should be while not_facing_north():

✅ How to Fix:

while facing_north():
while not_facing_north():
                    

Why: Karel should keep turning left UNTIL facing north, not WHILE already facing north.

Teaching Tip: This is a logic error that won't produce an error message but will cause incorrect behavior. Have students trace through what happens with the wrong condition.

Error #2 Line 13

⚠️ LOGIC ERROR: Duplicate Action

What's Wrong: There is an extra put_ball() inside the while loop

✅ How to Fix:

Remove the duplicate put_ball() statement. The correct structure should be:

while front_is_clear():
    put_ball()
    move()
    put_ball()

while front_is_clear():
    put_ball()
    move()
                    

Why: This causes Karel to place two balls per square, which is incorrect.

Error #3 Line 17

⚠️ SYNTAX ERROR: Missing Underscore

Error Message: NameError: name 'buildtower' is not defined

What's Wrong: Function name is buildtower() but should be build_tower()

✅ How to Fix:

buildtower()
build_tower()
                    

Teaching Tip: Function names must match EXACTLY, including underscores. Python is case-sensitive and space-sensitive.

Random Hurdles

5 Errors

Error #1 Line 8

⚠️ SYNTAX ERROR: Colon Instead of Parenthesis

Error Message: SyntaxError: invalid syntax

What's Wrong: turn_right(): should be turn_right() (no colon)

✅ How to Fix:

    turn_right():
    turn_right()
                    

Why: Colons are only used after function definitions, loops, and conditionals, not when calling functions.

Error #2 Lines 9-10

⚠️ SYNTAX ERROR: Incorrect Indentation

Error Message: IndentationError: unexpected indent

What's Wrong: Lines 9-10 are indented as if they're inside a block, but there's no reason for them to be indented

✅ How to Fix:

    turn_right():
        move()
        turn_right()

    turn_right()
    move()
    turn_right()
                    

Why: These commands should all be at the same indentation level within the jump_hurdle() function.

Teaching Tip: This error was caused by the colon on line 8. Once the colon is removed, the indentation also needs to be fixed.

Error #3 Before Line 6

⚠️ SYNTAX ERROR: Missing Function Definition

Error Message: NameError: name 'turn_right' is not defined

What's Wrong: The turn_right() function is never defined

✅ How to Fix:

Add the function definition before jump_hurdle():

def turn_right():
    turn_left()
    turn_left()
    turn_left()
                    

Error #4 Line 14

⚠️ LOGIC ERROR: Incorrect Range

What's Wrong: for i in range(14): should be for i in range(13):

✅ How to Fix:

for i in range(14):
for i in range(13):
                    

Why: Karel needs to move 13 times to cross 14 columns (moves between columns, not on them). This will cause Karel to crash into the wall.

Teaching Tip: This is the "fence post problem" - if you have 14 fence posts, you only need 13 sections of fence between them.

Error #5 Line 17

⚠️ SYNTAX ERROR: Incorrect Else Syntax

Error Message: SyntaxError: invalid syntax

What's Wrong: else front_is_clear(): should be just else:

✅ How to Fix:

    else front_is_clear():
    else:
                    

Why: The else statement doesn't take a condition. It automatically handles all cases not covered by the if statement.

Teaching Tip: If students want to check a second condition, they should use elif, not else.

Error #6 Line 18

⚠️ SYNTAX ERROR: Incorrect Indentation

Error Message: IndentationError: expected an indented block

What's Wrong: move() needs to be indented to be inside the else block

✅ How to Fix:

    else:
move()

    else:
        move()
                    

Why: After a colon in Python, the next line(s) must be indented to show they belong to that block.

📊 Error Summary

Total Errors Across All Problems: 9

Syntax Errors: 6 (Missing definitions, incorrect colons, indentation, function names)
Logic Errors: 3 (Wrong conditions, incorrect range, duplicate actions)

🐛 Debugging Answer Key - Teacher Guide

📚 Main Learning Objective:

Lots of Hurdles

Big Tower

Random Hurdles

📊 Error Summary