python modify __metaclass__ for whole program

Question

EDIT: Note that this is a REALLY BAD idea to do in production code. This was just an interesting thing for me. Don't do this at home!

Is it possible to modify __metaclass__ variable for whole program (interpreter) in Python?

This simple example is working:

class ChattyType(type):
    def __init__(cls, name, bases, dct):
        print "Class init", name
        super(ChattyType, cls).__init__(name, bases, dct)

__metaclass__= ChattyType


class Data:
    pass

data = Data() # prints "Class init Data"
print data

but I would love to be able change of __metaclass__ to work even in submodules. So for example (file m1.py):

 class A:
       pass

 a=A()
 print a

file main.py:

class ChattyType(type):
    def __init__(cls, name, bases, dct):
        print "Class init", name
        super(ChattyType, cls).__init__(name, bases, dct)

__metaclass__= ChattyType

import m1 # and now print "Class init A"

class Data:
    pass

data = Data() # print "Class init Data"
print data

I understand that global __metaclass__ is no longer working in Python 3.X, but that is not my concern (my code if proof of concept). So is there any way to accomplish this in Python-2.x?

Answer 1

The "global __metaclass__" feature of Python 2 is designed to work per-module, only (just think what havoc it would wreak, otherwise, by forcing your own metaclass on all library and third-party modules that you imported from that point onwards -- shudder!). If it's very important to you to "secretly" alter the behavior of all modules you're importing from a certain point onwards, for whatever cloak-and-dagger reason, you could play very very dirty tricks with an import hook (at worst by first copying the sources to a temporary location while altering them...) but the effort would be proportionate to the enormity of the deed, which seems appropriate;-)