Lib/functools.py

cpython 3.14 @ ab2d84fe1023/Lib/functools.py ↗

Lib/functools.py re-exports from _functools (C extension) and adds pure-Python utilities: wraps, total_ordering, cached_property, singledispatch, and singledispatchmethod.

Map

Lines	Symbol	Role
1-80	Re-exports from _functools	partial, reduce, lru_cache, cmp_to_key
81-160	wraps, update_wrapper	Copy function metadata to a wrapper
161-300	total_ordering	Fill in __lt__/__gt__/__le__/__ge__ from one defined method
301-500	cached_property	Lazy attribute computed once, stored in __dict__
501-700	singledispatch	Type-based dispatch with register() and MRO fallback
701-980	singledispatchmethod	singledispatch for methods with classmethod support

Reading

update_wrapper

update_wrapper(wrapper, wrapped) copies __module__, __name__, __qualname__, __annotations__, __doc__, and __dict__ from wrapped to wrapper, and sets __wrapped__ = wrapped. @wraps(f) is functools.update_wrapper(wrapper, f) as a decorator.

# CPython: Lib/functools.py:68 update_wrapper
def update_wrapper(wrapper, wrapped, ...):
    for attr in assigned:
        try:
            value = getattr(wrapped, attr)
        except AttributeError:
            pass
        else:
            setattr(wrapper, attr, value)
    ...
    wrapper.__wrapped__ = wrapped
    return wrapper

total_ordering

@total_ordering inspects the class for which comparison methods are defined and adds the missing ones. It builds a dispatch table mapping each missing method to an expression using the defined one (e.g. __gt__ from __lt__: return NotImplemented if result is NotImplemented else not result and self != other).

cached_property

cached_property(func) is a non-data descriptor. On first access, it calls func(self) and stores the result directly in self.__dict__[attrname], shadowing the descriptor for all subsequent accesses.

singledispatch MRO fallback

singledispatch maintains a dispatch_cache dict from type to implementation. On cache miss, it walks the type's MRO looking for a registered type. Virtual subclasses (via register) are checked before the MRO walk.

gopy notes

module/functools/ partially implements this. wraps and update_wrapper are ported. total_ordering requires __dict__ attribute writing on class objects. cached_property requires a non-data descriptor with __dict__ storage. singledispatch is planned.