what is the difference between functools.wraps and update_wrapper

Question

I am not able to find what is the difference between these two python functions.

functools.wraps and update_wrapper

Can some give me some code example so that i can understand what is the difference

Answer 1

functools.wraps is equivalent to:

def wraps(wrapped, assigned=WRAPPER_ASSIGNMENTS, updated=WRAPPER_UPDATES):     def decorator(wrapper):         return update_wrapper(wrapper, wrapped=wrapped, ...)     return decorator 

It's actually implemented using partial instead of an inner function, but the effect is the same.

The purpose is to allow using it as a decorator:

 @wraps(f)  def g():      ... 

is equivalent to:

def g():     ... g = update_wrapper(g, f) 

Answer 2

Normally you will just use wraps, which wraps *update_wrapper* . More:

• partial ing a function = create a new function with some arguments bound to values

• wraps partials *update_wrapper* with wrapped, thus creating a decorator for wrapper

• *update_wrapper* 's purpose is to copy certain attributes (not arguments) from wrapped to wrapper. On default these are:

 WRAPPER_ASSIGNMENTS = ('__module__', '__name__', '__qualname__', '__doc__',                        '__annotations__') WRAPPER_UPDATES = ('__dict__',) 

A useful example:

try:     from itertools import izip_longest as zip_longest except:     from itertools import zip_longest from collections import Iterable from functools import wraps  def ziplongest(*args):     '''zip_longest with last element as filler     >>> args=([9],[2,3],1)     >>> [t for t in ziplongest(*args)]     [(9, 2, 1), (9, 3, 1)]      '''     iterable = lambda a:(a if isinstance(a,Iterable) else [a])     _args = [iterable(a) for a in args]     withnone = zip_longest(*_args)     for e in withnone:         yield tuple((en or _args[i][-1]) for i,en in enumerate(e))  def listable(f):     '''apply f to list members     >>> @listable     ... def mul(a,b):     ...     'returns a*b'     ...     return a*b     >>> mul(2,[3,9])     [6, 18]     >>> mul.__doc__     'returns a*b'      '''     @wraps(f)#without this e.g __doc__ would get hidden     def to_elems(*args,**kwargs):         if any(isinstance(x,list) for x in args):             return [f(*a,**kwargs) for a in ziplongest(*args)]         else:             return f(*args,**kwargs)     return to_elems