Variables — Exercise Cards (Class room version)

Try me

How to use

• Each card below mirrors the A4 activity prompt. First try to complete the exercise by yourself, predict the output or find the bug before running.

• Then run the code cell to verify, or run the Fix cell (when provided) to see a correct version.

• Keep explanations short and schematic (what/why). ### Rendering Gemini into an interactive AI tutor

• If you need help, hints, or extra exercises from AI, use the following prompt to convert it into an AI-tutor

You are a **coding tutor** for Python in Jupyter/Colab. Follow the **course motto** “do not give up learning.”

### Role & Goals
- Use **Socratic guidance** and **test-first thinking** to help me solve problems myself.
- Help me read errors, reason about state, and make small, safe iterations.

### Strict Rules
1) **Do not** provide full working solutions or paste complete functions/programs.
   - You may show **tiny illustrative fragments (≤3 lines)** or **pseudo-code with TODOs**, but not a drop-in answer.
2) Prefer **questions over answers**; offer **one small next step** at a time.
3) When debugging, explain **what the traceback says**, give **2–3 hypotheses**, and propose the **smallest diff** in *plain English* first.
4) Encourage **TDD**: ask me to write/assert a test, predict, run, and report outputs.
5) Keep responses concise (≈120–150 words) unless I ask for a deeper explanation or code review.
6) Ask me to **run code and share results**; adapt based on the output.
7) If I request the full solution, remind me of the rules and offer a **higher-tier hint** instead.
8) When I finalize an exercise, reinforce learning lessons and suggest additional exercises

### Interaction Loop (use this structure)
- **Restate goal:** what I’m trying to accomplish in one line.
- **Diagnose:** key assumption to check or error to interpret.
- **Hint (tiered):**
  - Tier 1: Conceptual nudge (no code).
  - Tier 2: Directed hint (identify line/construct to change).
  - Tier 3: Pseudo-code with TODOs or a **1–3 line** pattern (still not a full solution).
- **Next action:** one concrete step for me to try now.
- **Ask back:** what to run/paste (output, test result, or traceback).

### When reviewing my code
- Comment on **correctness, clarity, naming, and complexity (big-O)**.
- Suggest **tests** I’m missing (boundaries, empty cases, error paths).

### Safety & Ethics
- No secrets or private data in prompts.
- avoid library functions/APIs unless I ask.

Stay in tutor mode for the whole session.

Numeric Operations

Card N-1 — Human Calculator

n = 9//2
n = n**2
# What is the value of n after the script?

# Card N-1 — check
n = 9//2
n = n**2
print(n)

Card N-2 — Human Calculator

# y = x % 2
# What is y when x=9? and when x=8?

# Card N-2 — check with two samples (no input)
def parity(x: int) -> int:
    return x % 2

print("x=9  -> y=", parity(9))
print("x=8  -> y=", parity(8))

Card N-3 — Code Detective (Find the bug)

Buggy Code:

x = ((1 + 2) * 3 / (4 - 0.5)

Fix it so it runs witout errors.

# Card N-3 — fixed
x = ((1 + 2) * 3 / (4 - 0.5)
print(x)

Card N-4 — Human Calculator

n = 9//2 - 2 ** 2
# What is the result?

# Card N-4 — check
n = 9//2 - 2 ** 2
print(n)

Card N-5 — Human Calculator

x = 4+5j
y = 3+3j
print(x.imag + y.imag)

What is printed?

# Card N-5 — check
x = 4+5j
y = 3+3j
print(x.imag + y.imag)

Strings

Card S-1 — Code Detective (Find the bug)

Buggy:

my_message = Hello World

Fix the string assignment.

# Card S-1 — fixed
my_message = Hello World
print(my_message)  # expected: Hello World

Card S-2 — Human Calculator

x = "2"
y = 3
print(x * y)

What is printed?

# Card S-2 — check
x = "2"
y = 3
print(x * y)

Original idea:

a = input("What did you say")
print(a + "- duh-duuh")

Question: What does the bot do? (We simulate without input.)

# Card S-3 — simulate without input
a = "I like Python"
print(a + "- duh-duuh")  # expected: echoes input with suffix

area = 9        # area covered
total = 10      # total area
print(f"Area = {area}, covered: {area/total:.0%}")

What is printed?

# Card S-4 — check
area = 9
total = 10
print(f"Area = {area}, covered: {area/total:.0%}")  # expected: Area = 9, covered: 90%

s = "Hello"
print(s + "!")
print(s.replace("l","L"))
print(s)

What is printed (and why)?

# Card S-5 — check
s = "Hello"
print(s + "!")               # Hello!
print(s.replace("l","L"))    # HeLLo
print(s)                     # Hello  (strings are immutable)

Boolean Variables

Card B-1 — Code Detective (Find the bug)

x = 1
y = 2
a = x = y  # a boolean variable?

Question: What’s wrong with the comment, and how to get a boolean instead?

# Card B-1 — explanation & fix
x = 1
y = 2
a = x = y
print(a, x, y)   # 2 2 2

Card B-2 — Human Calculator

Original idea (uses input):

age = int(input("what is your age?"))
print(18 <= age < 65)
print(bool(""))
print(bool("False"))

What gets printed? (Assume user enters the number 18.)

# Card B-2 — simulate without input
age = int(input("What is your age? "))
print(18 <= age < 65)  # expected: True
print(bool(""))        # expected: False (empty string is falsey)
print(bool("False"))   # expected: True (non-empty strings are truthy)

Card B-3 — Human Calculator

def ping():
    print("ping")
    return True
print(False and ping())
print(True or ping())

What is printed?

# Card B-3 — check (short-circuit)
def ping():
    print("ping")
    return True

print(False and ping())  # expected: False   (ping not called)
print(True or ping())    # expected: True    (ping not called)

D) Extra Cards

Extra N-E1 — Human Calculator

print(2 ** 1 + 2)

What is printed, and why?

# Extra N-E1 — check (operations priority)
print(2 ** 1 + 2)

Fix the code below to parse the string s ="3.14" into a number.

# Extra N-E2 — demo
s = "3.14"
# print(int(s))  # ValueError if uncommented
val =  3.4 # FIX: correct approach: parse as float
print(val)       # expected: 3.14

print(f"bin:{13:b} hex:{255:x}")

What is printed?

# Extra S-E4 — check
print(f"bin:{13:b} hex:{255:x}")  # expected: bin:1101 hex:ff

a = 1000; b = 1000
print(a == b, a is b)

What is printed, and why?

# Extra B-E5 — check
a = 1000; b = 1000
print(a == b, a is b)  # expected: True False (typically; equal value, different objects)

Predict the outputs:

print(bool([]), bool([0]))
print(bool({}), bool({"x":0}))

# Extra B-E6 — check
print(bool([]), bool([0]))       # expected: False True
print(bool({}), bool({"x":0}))   # expected: False True

Avoid using is for string equality.

code = "OK"
# if code is "OK":   # anti-pattern
#     print("ok")

Fix it.

# Extra B-E7 — fixed
code = "OK"
if code == "OK":
    print("ok")  # expected: ok

Extra B-8 — Human Calculator Predict the result

print(True and True)
print(not False or False)
print(3 == 4)
print(0.3 == 0.1 + 0.2)

print(True and True)
print(not False or False)
print(3 == 4)
print(0.3 == 0.2 + 0.1)