Advanced Language Features

A few features that show up constantly in real Python codebases once past the basics:

# Decorators: wrap a function to add behavior around it
def log_calls(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__}")
        return func(*args, **kwargs)
    return wrapper

@log_calls
def add(a, b):
    return a + b

add(2, 3)   # prints "Calling add", then returns 5

# Context managers: the "with" statement's underlying protocol
class Timer:
    def __enter__(self):
        print("Started")
        return self

    def __exit__(self, *args):
        print("Stopped")

with Timer():
    print("Working...")

@log_calls is Python's decorator syntax — shorthand for add = log_calls(add). Any class implementing __enter__/__exit__ can be used with with, the same protocol open() uses under the hood.