Python 3.8+functoolsterm

functools.cached_property

caching

Computes the value of a property once and stores it in the instance's __dict__. Later accesses return the cached value without calling the method.

Syntax

@functools.cached_property

The cache never invalidates itself: if the object's fields change, the property keeps returning the stale value until you delete it with del obj.area. It needs a normal instance __dict__, so a class with __slots__ will not work — there is nowhere to store the value. Since Python 3.12 there is no shared lock, so under threads the computation may run more than once.

Examples

from functools import cached_property
class Circle:
    def __init__(self, r): self.r = r
    @cached_property
    def area(self):
        return 3.14159 * self.r ** 2
c = Circle(5)
print(c.area)  # → 78.53975
print(c.area)  # → 78.53975  (без вычисления)
print('area' in c.__dict__)  # → True
print(type(c.__dict__['area']))  # → <class 'float'>

See also

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