`functools`

Tools for working with functions and callables: caches, partial application, reduction, single-dispatch, and decorator helpers.

Source-of-record: Lib/functools.py, Modules/_functoolsmodule.c, functools docs.

Caching

Function	Returns
`@functools.cache`	Unbounded `lru_cache(maxsize=None)`.
`@functools.lru_cache(maxsize=128, typed=False)`	Bounded LRU cache decorator.
`@functools.cached_property`	Compute once, store on instance.

Cache info: .cache_info() returns CacheInfo(hits, misses, maxsize, currsize). .cache_clear() empties. .cache_parameters() returns the kwargs.

functools.reduce(function, iterable, initializer=missing)

Folds left. initializer provides the seed; without it the first iterable element seeds.

Class / function	Effect
`functools.partial(func, /, args, *kw)`	Pre-bind positional and keyword args.
`functools.partialmethod(func, /, args, *kw)`	Same, but as a descriptor for class bodies.

Attributes: .func, .args, .keywords.

API	Role
`@functools.singledispatch`	Generic function dispatched on first arg type.
`fn.register(type)(impl)`	Register an implementation.
`fn.dispatch(cls)`	Pick the impl for `cls`.
`fn.registry`	Mapping of type to impl.
`@functools.singledispatchmethod`	Same, as a method.

Helper	Role
`functools.wraps(wrapped, ...)`	Copy metadata onto a wrapper.
`functools.update_wrapper(wrapper, wrapped, assigned=WRAPPER_ASSIGNMENTS, updated=WRAPPER_UPDATES)`	The underlying logic.
`WRAPPER_ASSIGNMENTS`	`(__module__, __name__, __qualname__, __annotations__, __doc__)`.
`WRAPPER_UPDATES`	`(__dict__,)`.

Helper	Role
`@functools.total_ordering`	Fill in the missing comparison methods given one of `__lt__`, `__le__`, `__gt__`, `__ge__` and `__eq__`.
`functools.cmp_to_key(cmp)`	Adapt a 3-way comparator for `key=`.

functools.reduce and functools.partial are both implemented in C for speed; Python equivalents live in Lib/functools.py.

Area	State
`cache`, `lru_cache`, `cached_property`	Complete.
`partial`, `partialmethod`	Complete; C-fast paths in `module/_functools`.
`singledispatch`	Complete.
`wraps`, `update_wrapper`, `total_ordering`, `cmp_to_key`	Complete.