Python functools.wraps equivalent for classes

user_99989 0
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When defining a decorator using a class, how do I automatically transfer over__name__, __module__ and __doc__? Normally, I would use the @wraps decorator from functools. Here's what I did instead for a class (this is not entirely my code):

class memoized:
    """Decorator that caches a function's return value each time it is called.
    If called later with the same arguments, the cached value is returned, and
    not re-evaluated.
    """
    def __init__(self, func):
        super().__init__()
        self.func = func
        self.cache = {}

    def __call__(self, *args):
        try:
            return self.cache[args]
        except KeyError:
            value = self.func(*args)
            self.cache[args] = value
            return value
        except TypeError:
            # uncacheable -- for instance, passing a list as an argument.
            # Better to not cache than to blow up entirely.
            return self.func(*args)

    def __repr__(self):
        return self.func.__repr__()

    def __get__(self, obj, objtype):
        return functools.partial(self.__call__, obj)

    __doc__ = property(lambda self:self.func.__doc__)
    __module__ = property(lambda self:self.func.__module__)
    __name__ = property(lambda self:self.func.__name__)

Is there a standard decorator to automate the creation of name module and doc? Also, to automate the get method (I assume that's for creating bound methods?) Are there any missing methods?

decorator python
6 Answers

Turns out there's a straightforward solution using functools.wraps itself:

import functools

def dec(cls):
    @functools.wraps(cls, updated=())
    class D(cls):
        decorated = 1
    return D


@dec
class C:
    """doc"""

print(f'{C.__name__=} {C.__doc__=} {C.__wrapped__=}')

$ python3 t.py 
C.__name__='C' C.__doc__='doc' C.__wrapped__=<class '__main__.C'>

Note that updated=() is needed to prevent an attempt to update the class's __dict__ (this output is without updated=()):

$ python t.py
Traceback (most recent call last):
  File "t.py", line 26, in <module>
    class C:
  File "t.py", line 20, in dec
    class D(cls):
  File "/usr/lib/python3.8/functools.py", line 57, in update_wrapper
    getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
AttributeError: 'mappingproxy' object has no attribute 'update'
user_8121830
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