Functions

Introduction

Functions are first-class objects in Python — pass them as arguments, return them, store them in collections. They support default args, keyword args, *args, **kwargs.

Understanding the topic

Core concepts to understand:

• def name(args):
• Default values: def f(x=10):
• Variadic: *args (tuple), **kwargs (dict).
• Return tuples for multiple values.

Syntax reference

Visual flow / code:

def greet(name: str, greeting: str = "Hello") -> str:
    return f"{greeting}, {name}!"

# Keyword args
greet(name="Alice", greeting="Hi")

# Variadic
def total(*nums: int, factor: int = 1) -> int:
    return sum(nums) * factor

total(1, 2, 3, factor=2)  # 12

# **kwargs
def config(**opts):
    print(opts)
config(host="localhost", port=8080)

Execution workflow

Real-world use

Functions with type hints + docstrings form the API contract of any Python codebase. Tools like Sphinx and mkdocs auto-generate docs from them.

Best practices

• Always add type hints.
• Default args must be immutable (avoid =[]).
• Keep functions small (~20 lines).

Common mistakes

• def f(x=[]): — mutable default arg shared across calls!

Hands-on exercise

Interview preparation — practice these questions:

• What's the mutable default arg trap?
• *args vs **kwargs?
• Can functions return functions?

Summary

In summary: Functions are first-class. Never use mutable defaults.