functools.wraps(func)(lambda *args, **kwargs: func(*args, **kwargs))

Decorators & Metaclasses

Meaning

functools.wraps copies essential attributes (__name__, __module__, __qualname__, __doc__, __annotations__) from the original function to the wrapper function. Without it, a decorator would hide the original function's identity, breaking introspection tools like help() and debugging. You reach for this pattern when you need to add behavior via a decorator while preserving the wrapped function's metadata.

Primary Function

Decorators

Communicative Purpose

Preserves function metadata and introspection capabilities when applying decorators.

Pattern

functools.wraps(original_func)(lambda *args, **kwargs: original_func(*args, **kwargs))

Core Structure

functools.wraps(...)(lambda ...: ...(...))

Função primária

Decorators

Propósito comunicativo

Preserves function metadata and introspection capabilities when applying decorators.

Situações de gatilho

Python: adding logging to functions without losing their __name__; Python: timing function execution while preserving help() output; Python: implementing authentication decorators that keep original signatures.

Contextos

Python standard library, web frameworks (Flask, Django), any Python project using decorators.

Padrão

functools.wraps(original_func)(lambda *args, **kwargs: original_func(*args, **kwargs))

Estrutura central

functools.wraps(...)(lambda ...: ...(...))

Slots de substituição

original_func: callable, args: tuple, kwargs: dict

Colocados típicos

@decorator syntax
def wrapper(*args
**kwargs):
functools.partial

Substituições comuns

Manual copying of __name__
__doc__
etc.: more verbose but avoids import
class-based descriptors: more flexible but heavier.

Erros comuns

Forgetting to import functools: causes NameError when wraps is referenced; using wraps without parentheses: results in TypeError because wraps expects a function argument; applying wraps to a class instead of a function: leads to AttributeError as classes lack __wrapped__; omitting *args, **kwargs in the wrapper: causes the decorated function to lose arguments; returning an incorrect value from the lambda: breaks the original function's behavior.

Similar / contraste

functools.partial: fixes arguments rather than preserving metadata; class decorators: modify class behavior instead of function metadata; closure-based decorators: similar pattern but require manual metadata copying.

Interferências

Coming from Java: may rely on annotations instead of wrapper functions — Python uses functools.wraps for metadata preservation; Coming from JavaScript: may assume function.name is immutable — Python's __name__ is mutable and needs wrapping.

Família do chunk

functools.partial
decorator syntax
closure decorators
class decorators

Nuance

Do not use when you need to alter the function signature, as wraps only copies selected attributes; the performance overhead is negligible, typically a few microseconds per call; wraps only copies __module__, __name__, __qualname__, __doc__, and __annotations__, leaving other attributes unchanged.

Efeito pragmático

Enables reliable debugging, introspection, and help() on decorated functions; prevents confusion in large codebases where decorators obscure function identity.

Dica de memória

Like giving an actor a costume that doesn't hide their face — the audience still knows who they are.

Upgrade path

Creating class-based decorators or using functools.singledispatch for more complex dispatch.

Frequência: HighFormulaicidade: Semi-fixedPrioridade de aquisição: Active recallPrioridade de output: BothTag de espaçamento: Medium-term