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MutatingDescriptor.py

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#This is prone to strange side effects and race conditions.

class MutatingDescriptor(object):

def __init__(self, func):

self.my_func = func

def __get__(self, obj, obj_type):

#Modified state is visible to all instances of C that might call "show".

self.my_obj = obj

return self

def __call__(self, *args):

return self.my_func(self.my_obj, *args)

def show(obj):

print (obj)

class C(object):

def __init__(self, value):

self.value = value

def __str__(self):

return ("C: " + str(self.value))

show = MutatingDescriptor(show)

c1 = C(1)

c1.show()

c2 = C(2)

c2.show()

c1_show = c1.show

c2.show

c1_show()

#Outputs:

#C: 1

#C: 2

#C: 2