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4.1 Functions in Python

Functions are defined with def and can use positional-only, positional-or-keyword, and keyword-only parameters.

Defining and returning values​

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

Parameter kinds​

def api(name, /, version, *, timeout=30):
    return name, version, timeout
  • Parameters before / are positional-only.
  • Parameters after * are keyword-only.

Defaults and common pitfall​

Default values are evaluated once at function definition time.

def append_item(item, items=None):
    if items is None:
        items = []
    items.append(item)
    return items

*args and **kwargs​

def log_event(event, *args, **kwargs):
    ...

Annotations and docstrings​

  • Function annotations are metadata and do not enforce runtime types.
  • Docstrings should summarize purpose and usage clearly.

Official references​