Functions & Scope

07 / 10 Part of python basic

⚡ Topic 06 · Reusability

Functions & Scope

Write reusable, composable functions with parameters, return values, default arguments, and lambda expressions.

⏱ ~45 min
🟡 Intermediate
🏗️ Essential

Defining & Calling Functions

Use the def keyword. Functions run only when called, and can return values with return.

functions.py

def greet(name):
    """Return a personalised greeting."""  # docstring
    return f"Hello, {name}!"

message = greet("Alice")
print(message)  # Hello, Alice!

Default & Keyword Arguments

Parameters can have default values, and callers can pass arguments by name for clarity.

defaults.py

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

print(power(3))                       # 9
print(power(2, 10))                   # 1024
print(power(exponent=3, base=4))     # 64

*args and **kwargs

Accept a variable number of positional (*args) or keyword (**kwargs) arguments.

args_kwargs.py

def total(*numbers):
    return sum(numbers)

print(total(1, 2, 3, 4))  # 10

def profile(**info):
    for key, val in info.items():
        print(f"{key}: {val}")

profile(name="Alice", age=30)

Lambda Functions

Lambda creates small, anonymous one-expression functions — great for use as arguments to sorted(), map(), and filter().

lambda.py

square = lambda x: x ** 2
print(square(5))  # 25

nums = [3, 1, 4, 1, 5]
sorted(nums, key=lambda x: -x)  # descending

Scope — the LEGB Rule

Python resolves variable names in this order: Local → Enclosing → Global → Built-in.

scope.py

x = "global"

def outer():
    x = "enclosing"
    def inner():
        x = "local"
        print(x)  # local
    inner()
    print(x)      # enclosing

outer()
print(x)          # global

💡 global & nonlocal keywords

Use global x inside a function to modify a global variable. Use nonlocal x to modify a variable in the enclosing (non-global) scope.

Menu

Functions & Scope

Defining & Calling Functions

Default & Keyword Arguments

*args and **kwargs

Lambda Functions

Scope — the LEGB Rule