Source code for bag.reify

"""Contains the invaluable @reify decorator, stolen from Pyramid."""

from functools import update_wrapper


[docs]class reify(object): """Substitute decorated method with its return value on 1st use. Use as a class method decorator. It operates almost exactly like the Python ``@property`` decorator, but it puts the result of the method it decorates into the instance dict after the first call, effectively replacing the function it decorates with an instance variable. It is, in Python parlance, a non-data descriptor. The following is an example and its usage:: >>> from bag.reify import reify >>> class Foo(object): ... @reify ... def jammy(self): ... print('jammy called') ... return 1 >>> f = Foo() >>> v = f.jammy jammy called >>> print(v) 1 >>> f.jammy 1 >>> # jammy func not called the second time; it replaced itself with 1 >>> # Note: reassignment is possible >>> f.jammy = 2 >>> f.jammy 2 """ def __init__(self, wrapped): self.wrapped = wrapped update_wrapper(self, wrapped) def __get__(self, inst, objtype=None): if inst is None: return self val = self.wrapped(inst) setattr(inst, self.wrapped.__name__, val) return val