Quia - Class Page - 2-Two Towers Challenge Teacher Answer Key

⚡ Quick Reference: All 3 Errors at a Glance

Error #	Line(s)	Error Type	Problem	Fix
1	Line 5	Syntax Error	Missing `def` keyword	Add `def` before `come_down():`
2	Line 6	Name Error	Function not defined	Must define `turn_around()` function
3	Lines 13, 16	Name Error	Function misspelled	Change `buildtower()` to `build_tower()`

1 Missing def Keyword

Syntax Error

❌ The Problem (Line 5):

come_down():
    turn_around()
    move()
    move()
    turn_left()

Why it's wrong: Python requires the def keyword to define a function. Without it, Python doesn't recognize this as a function definition.

👏

Gesture: Clap (broken code - missing symbol)

✅ The Fix:

def come_down():
    turn_around()
    move()
    move()
    turn_left()

What students should explain: "The function definition is missing the def keyword. Python needs def to know we're creating a function."

2 Undefined Function Called

Name Error

❌ The Problem (Line 6):

def come_down():
    turn_around()    # ← This function is NOT defined!
    move()
    move()
    turn_left()

Why it's wrong: The turn_around() function is called but never defined in the starter code. Python cannot execute a function that hasn't been defined.

🤷

Gesture: Point & Shrug (Who's that? - undefined name)

✅ The Fix - Students must ADD this function:

def turn_around():
    turn_left()
    turn_left()

⚠️ Teaching Note: This is the trickiest error! Students must realize they need to CREATE a missing function, not just fix existing code.

3 Misspelled Function Name

Name Error

❌ The Problem (Lines 13 AND 16 - appears TWICE!):

move()
buildtower()        # ← Line 13: Missing underscore!
come_down()
move()
move()
buildtower()        # ← Line 16: Missing underscore again!
move()
turn_right()

Why it's wrong: The function is defined as build_tower() (with underscore) but called as buildtower(). Python is case-sensitive and treats these as different names.

🤷

Gesture: Point & Shrug (Who's that? - misspelled name)

✅ The Fix (in TWO places!):

move()
build_tower()       # ← Added underscore
come_down()
move()
move()
build_tower()       # ← Added underscore
move()
turn_right()

⚠️ Common Mistake: Many students will fix line 13 but forget line 16. Remind them: "How many times is build_tower() called?"

⏱️ Time Management for 6-Minute Check

Minutes 1-2: Quick scan - did they find all 3 error locations?
Minutes 3-4: Check error type classification
Minute 5: Verify they CREATED turn_around() function
Minute 6: Provide quick feedback and stamp/initial

💡 Teaching Tips & Common Mistakes

🎯 For Error #1

"What keyword does Python need to define a function?"
"What's missing from this line?"
Watch for: Students adding def in wrong place

🎯 For Error #2

"Does this function exist anywhere in the code?"
"What would Karel need to do to turn around?"
Watch for: Students marking it but not writing the solution

🎯 For Error #3

"How is the function name spelled when it's defined vs. called?"
"Are there any other places this function is called?"
Watch for: Only fixing one instance

📊 Expected Performance

Strong: Finds all 3 errors in 3-4 minutes
Developing: Finds 2 errors, needs prompting
Needs Support: Finds only Error #3

🌟 Extension for Early Finishers

"Why do you think the turn_around() function is missing?"
"Could you create a turn_right() function a different way?"
"What would happen if you only fixed line 13 but not line 16?"

✨ Complete Solution Code

Total Errors: 3 errors (but Error #3 appears twice, so 4 corrections needed)

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

def turn_around():              # ← ERROR #2: This was missing!
    turn_left()
    turn_left()

def come_down():                # ← ERROR #1: Was missing 'def'
    turn_around()
    move()
    move()
    turn_left()

def build_tower():
    turn_left()
    put_ball()
    move()
    put_ball()
    move()
    put_ball()

move()
build_tower()                   # ← ERROR #3: Was 'buildtower()'
come_down()
move()
move()
build_tower()                   # ← ERROR #3: Was 'buildtower()'
move()
turn_right()

📝 Summary of All Changes

Added: def turn_around(): function (completely missing)
Fixed: Added def keyword to come_down(): function
Fixed: Changed buildtower() to build_tower() on line 13
Fixed: Changed buildtower() to build_tower() on line 16

🗼 Two Towers Challenge