What is wrong with this simple python metaclass? -

digression start

i learnt metaclasses in python. don't think creators of python wanted use them. mean name metaclass might not class in cases enough divert people away concept!

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on question. wrote simple metaclass add default doc string classes created in module. not working:

def metest(cls,name,bases,dict):     cls.setattr(cls,'__doc__',"""default doc""")     return type(cls,(),{})  __metaclass__=metest  class test(object):     pass  print test.__doc__  t=test()  print t.__doc__ 

output:

none none 

what doing wrong?

i made example work:

def metest(name, bases, dict):     print name, bases, dict     dict['__doc__'] = """new doc"""     cls = type(name+"_meta", bases, dict)     return cls  class test(object):     "old doc"     __metaclass__ = metest  print test print test.__doc__  t = test()  print t.__doc__ 

1. make "meta class" used.
2. correct signature of "class creation function". cls created us.
3. have "old" , "new" docstring in order distinguish.