Functions & Parameters

Intermediate Python
def*args**kwargsdecoratorslambdatype hints

Objective

Write functions with various parameter types, use decorators, and add type annotations.

Tools & Technologies

  • def
  • *args
  • **kwargs
  • decorators
  • lambda
  • type hints

Key Commands

def func(*args, **kwargs):
@functools.wraps
lambda x: x**2
def greet(name: str) -> str:
functools.partial

Architecture Overview

graph LR CALL[greet name='Alice' title='Dr'] -->|positional| P[positional\nparams] CALL -->|keyword| K[keyword\nparams] CALL -->|extra pos| A[*args\ntuple] CALL -->|extra kw| KW[**kwargs\ndict] P --> FUNC[Function body] K --> FUNC A --> FUNC KW --> FUNC FUNC --> RET[return value] style FUNC fill:#1a1a2e,stroke:#00d4ff,color:#e0e0e0

Step-by-Step Process

01
Parameter Types

Understand all ways to pass arguments.

def create_user(name, age, *, admin=False, **extra):
    # name, age = positional required
    # admin = keyword-only (after *)
    # extra = catch-all keyword args
    print(name, age, admin, extra)

create_user('Alice', 25)
create_user('Bob', 30, admin=True, dept='Engineering')

# *args and **kwargs
def log(*args, **kwargs):
    print(args, kwargs)
02
Decorators

Functions that wrap other functions.

import functools, time

def timer(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        print(f'{func.__name__} took {time.time()-start:.3f}s')
        return result
    return wrapper

@timer
def slow_function():
    time.sleep(0.1)
    return 42
03
Type Hints

Add type annotations for better tooling and documentation.

from typing import Optional, Union, List

def greet(name: str, times: int = 1) -> str:
    return ('Hello, ' + name + '! ') * times

def find_user(user_id: int) -> Optional[dict]:
    # Returns dict or None
    ...

def process(data: Union[str, bytes]) -> List[str]:
    ...

Challenges & Solutions

  • Mutable default arguments are shared across calls: def f(lst=[]): — use None instead
  • functools.wraps preserves function metadata through decoration — always include it

Key Takeaways

  • @staticmethod and @classmethod serve different purposes — understand both
  • Type hints are not enforced at runtime but enable mypy static checking