Adv Python — Closure

Survey Nested Functions

Read 3 examples and trace scope/captured values.

1 · Formatter

def report(title, values):
    def normalize(v):
        def label(x):
            return f"{title}: {x}"
        return label(round(v, 2))
    return [normalize(v) for v in values]

2 · Validation

def checkout(limit):
    def validate(amount):
        def remaining():
            return limit - amount
        return amount <= limit, remaining()
    return validate

3 · Nested state

def session(user):
    attempts = 0
    def login(password):
        def audit(ok):
            return user, attempts, ok
        return audit(password == "demo")
    return login

Learning Survey

Identify outer/inner scope Identify captured values Recognize reading/debug path complexity Ready to use closure for retained behavior/state

Implement Closure

A · Greeter

make_greeter(prefix) returns inner greet(name).

Hello, KASA!

B · Multiplier

Capture factor in make_multiplier().

triple(7) → 21

C · Counter

Retain state with nonlocal.

start 10 → 11 → 12

Python Workspace

PYTHON CONSOLE Ready.

Using Closure — Caller First

The caller is fixed. Design a closure that supports it.

member_price = make_price_rule(0.10)
print(member_price(1000))
print(member_price(2500))
print(member_price(500))

Expectation
900.0
2250.0
450.0

Capture discount; the returned function receives amount.

Your Closure

PYTHON CONSOLE Ready.

Apply Closure with OOP

TicketService Validator Factory

The object owns service identity. A method creates a closure configured with a minimum amount. The closure remembers accepted-count state.

Implement constructor.
Implement make_validator(minimum).
Create accepted = 0 in enclosing scope.
Return validate(amount).
Use nonlocal accepted.

KASA: REJECT amount=50
KASA: ACCEPT #1 amount=120
KASA: ACCEPT #2 amount=300

Build It

PYTHON CONSOLE Ready.