While executing the code below, I'm getting AttributeError: attribute '__doc__' of 'type' objects is not writable.
from functools import wraps
def memoize(f):
""" Memoization decorator for functions taking one or more arguments.
Saves repeated api calls for a given value, by caching it.
"""
@wraps(f)
class memodict(dict):
"""memodict"""
def __init__(self, f):
self.f = f
def __call__(self, *args):
return self[args]
def __missing__(self, key):
ret = self[key] = self.f(*key)
return ret
return memodict(f)
@memoize
def a():
"""blah"""
pass
Traceback:
AttributeError Traceback (most recent call last)
<ipython-input-37-2afb130b1dd6> in <module>()
17 return ret
18 return memodict(f)
---> 19 @memoize
20 def a():
21 """blah"""
<ipython-input-37-2afb130b1dd6> in memoize(f)
7 """
8 @wraps(f)
----> 9 class memodict(dict):
10 """memodict"""
11 def __init__(self, f):
/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/functools.pyc in update_wrapper(wrapper, wrapped, assigned, updated)
31 """
32 for attr in assigned:
---> 33 setattr(wrapper, attr, getattr(wrapped, attr))
34 for attr in updated:
35 getattr(wrapper, attr).update(getattr(wrapped, attr, {}))
AttributeError: attribute '__doc__' of 'type' objects is not writable
Even though the doc string is provided, I don't know what's wrong with this.
It's works fine if not wrapped, but I need to do this.
@wraps(f) is primarily designed to be used as a function decorator, rather than as a class decorator, so using it as the latter may lead to the occasional odd quirk.
The specific error message you're receiving relates to a limitation of builtin types on Python 2:
>>> class C(object): pass
...
>>> C.__doc__ = "Not allowed"
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: attribute '__doc__' of 'type' objects is not writable
If you use Python 3, switch to a classic class in Python 2 (by inheriting from UserDict.UserDict rather than the dict builtin), or use a closure to manage the result cache rather than a class instance, the decorator will be able to copy the docstring over from the underlying function.