Functions & Variable Lifecycle — Code Cards (Classroom Version)¶

Try me¶

How to use¶

Each card mirrors an A4 classroom prompt. Predict first (or discuss), then run the cell to check.
Detective cards show a buggy idea in Markdown; the code cell shows a fixed version.
Keep explanations short and schematic (what → why).

Turn Gemini into a coding tutor (no direct answers)¶

Paste this in your first chat with Gemini to keep it in “tutor mode”:

You are a coding tutor for Python in Jupyter/Colab. Follow the course motto “do not give learning.”
Role: Use Socratic guidance and test‑first thinking so I solve problems myself.

Rules
1) Do NOT provide full working solutions. Show at most tiny fragments (≤3 lines) or TODO-style pseudocode.
2) Prefer questions over answers; offer one small next step at a time.
3) When debugging, read the traceback, give 2–3 hypotheses, propose the smallest change in plain English.
4) Encourage TDD: ask me to write an assert, predict, run, and report results.
5) Keep replies concise (≈120–150 words) unless I ask for deep dives.
6) Ask me to run code and share output; adapt based on results.
7) If I request the full solution, remind me of the rules and offer a higher‑tier hint instead.

Key Concepts¶

Card KEY-1 — Code Wizard (Answer the question)¶

Is x = len("abc") an expression or a statement? Why?

(Discuss; then run to inspect the value.)

[ ]:

# KEY-1 — inspect
x = len("abc")

Card KEY-2 — Code Wizard (Answer the question)¶

Is y = abs(-8) a function call, a variable assignment statement, or both? Explain in your own words.

(Discuss; then run to inspect the value.)

[ ]:

# KEY-2 — inspect
y = abs(-8)

Function Definition & Calls¶

Card FUN-1 — Code Wizard (Fix the code)¶

Fix the code to define a variable x, assign "Hasta la vista baby", and print

x = print("Hasta la vista baby")

[ ]:

# FUN-1 — Fix!
x = print("Hasta la vista baby")

Card FUN-2 — Code Wizard (Fix the code)¶

Define a polynomial function f(x) = x^2 + 2x + 1 that returns the value. Then call f(3).

# FUN-2 — Fix!
def f(x):
    y = x**2 + 1
print(f(3)) ## Expected 16

[ ]:

# FUN-2 — Fix!
def f(x):
    y = x**2 + 1
print(f(3)) ## Expected 16

Card FUN-3 — Predict the output (default used vs overridden)¶

def greet(name, punctuation="!"):
    return f"Hello, {name}{punctuation}"

print(greet("Ada"))
print(greet("Ada", "?"))
print(greet(name="Grace"))

Question: What three lines are printed? Why?

[ ]:

# FUN-3 — run to check
def greet(name, punctuation="!"):
    return f"Hello, {name}{punctuation}"

print(greet("Ada"))           # default "!" used
print(greet("Ada", "?"))      # override default
print(greet(name="Grace"))    # keyword uses default

Card FUN-4 — Predict the Output (positional & keyword)¶

def power(base, exp=2):
    return base ** exp

print(power(3))
print(power(2, 3))
print(power(exp=3, base=2))

Question: Predict the three numbers and explain which call used the default.

[ ]:

# DEF-2 — run to check
def power(base, exp=2):
    return base ** exp

print(power(3))
print(power(2, 3))
print(power(exp=3, base=2))

Card FUN-5 — Code Detective (mutable default trap)¶

Buggy idea:

def add_item(x, bag=[]):
    bag.append(x)
    return bag

Task: Explain the bug and fix so repeated calls don’t share state. (Hint: WHat happens if bag is None)

[ ]:

def add_item(x, bag=[]):
    bag.append(x)
    return bag

print(add_item("a"))
print(add_item("b"))
print(add_item("c", None))

Card FUN-6 — Mini‑Design: totals with defaults (tax & discount)¶

Complete the code below to complete function total(price, qty=1, tax=0.21, discount=0.0) that returns the final price after applying discount first, then tax: final = price * qty * (1 - discount) * (1 + tax)

Calls to predict:

print(total(10))
print(total(10, qty=3))
print(total(10, tax=0.10, discount=0.20))
print(total(price=10, discount=0.10, qty=2, tax=0.21))

[ ]:

# FUN-6 — reference implementation & checks
def total(price, qty=1, tax=0.21, discount=0.0):
    """Return final cost after discount then tax."""

print(total(10))                                  # 12.1
print(total(10, qty=3))                           # 36.3
print(total(10, tax=0.10, discount=0.20))         # 8.8
print(total(price=10, discount=0.10, qty=2, tax=0.21))  # 21.78

Card FUN7 — Code Wizard (Return vs Print)¶

Consider:

def area(w, h):
    print(w * h)
a = area(3, 4)

Question: What is stored in a? Refactor to return the value and print at the call site.

[ ]:

def area(w, h):
    #TODO: Fix to return the area

a = area(3, 4)
print("Area:", a)  # Expected: Area: 12

Card FUN-7 — Code Wizard Challenge (write & call with mixed arguments)¶

Write rectangle(w, h=1, unit="cm") -> str that returns a formatted string like "3x4 cm".

Then call it as:

print(rectangle(3, 4)) # Expected 3x4 cm
print(rectangle(5))    # Expected 5x1 cm
print(rectangle(h=2, w=7, unit="mm")) # Expected 2x7 cm

[ ]:

# DEF-7 — reference solution
def rectangle(w, h=1, unit="cm"):
    #TODO: Complete

print(rectangle(3, 4))                 # 3x4 cm
print(rectangle(5))                    # 5x1 cm
print(rectangle(h=2, w=7, unit="mm"))  # 7x2 mm