Preserve function metadata when creating wrapper functions (e.g., decorators).

Explain how to retain original function attributes when wrapping a function.

When writing a decorator or wrapper that should not obscure the wrapped function's identity for debugging, help, or serialization.

Used in decorator factories, for web frameworks, logging decorators that decorators, middleware wrappers, or any function‑wrapping scenario where introspection (e.g., __name__, __module__) must stay intact.

functools.update_wrapper(wrapper, func, assigned=tuple, updated=tuple)

wrapper: any callable wrapper object; func: the original function to copy attributes from; assigned: tuple of attribute names to copy; updated: tuple of attribute names to update (e.g., '__dict__').

• functools
• wraps
• decorator
• wrapper
• __module__
• __name__
• __qualname__
• __dict__

• functools.wraps (which internally calls update_wrapper with default args).

Forgetting to copy __module__ or __qualname__, leading to misleading tracebacks; swapping wrapper and func arguments.

functools.wraps (decorator form), functools.update_wrapper (function form), manual attribute copying.

Do not confuse update_wrapper with wraps; the former returns the wrapper, the latter returns a decorator.

• functools.wraps
• functools.update_wrapper
• decorator patterns

Only copies the attributes listed in assigned/updated; any other attributes remain unchanged on the wrapper.

Preserves introspection metadata, making decorated functions behave like the original for help(), logging, and serialization.

Think of update_wrapper as ‘copy the name tag’ from the original function to your wrapper.

The updated tuple is empty here, meaning no attributes are updated (only assigned).

Learn functools.wraps for a more convenient decorator form.