Reminder of how Python metaclasses work

metafu.py

offset=[0]

def log(f):
    def wrap(*args, **kwds):
        tab = '\t'*offset[0]
        print tab, f, args, kwds
        offset[0] += 1
        ret = f(*args, **kwds)
        print tab, f, ' () -> ', ret
        offset[0] -= 1
        return ret
    return wrap

class Meta(type):
    @log
    def __new__(mcs, name, bases, dikt):
        return super(Meta, mcs).__new__(mcs, name, bases,dikt)
    @log
    def __init__(cls, name, bases, dikt):
        return super(Meta, cls).__init__(name, bases, dikt)
    @log
    def __call__(cls, *args, **kwds):
        return super(Meta, cls).__call__(*args, **kwds)

print 'defining class'

class Type(object):
    __metaclass__ = Meta
    @log
    def __new__(cls, *args, **kwds):
        return super(Type, cls).__new__(cls, *args, **kwds)
    @log
    def __init__(self, *args, **kwds):
        pass

print 'creating instance'

t = Type()

"""
Output of this is:

defining class
 <function __new__ at 0x2740f50> (<class '__main__.Meta'>, 'Type', (<type 'object'>,), {'__module__': '__main__', '__metaclass__': <class '__main__.Meta'>, '__new__': <function wrap at 0x2743140>, '__init__': <function wrap at 0x27438c0>}) {}
 <function __new__ at 0x2740f50>  () ->  <class '__main__.Type'>
 <function __init__ at 0x27432a8> (<class '__main__.Type'>, 'Type', (<type 'object'>,), {'__module__': '__main__', '__metaclass__': <class '__main__.Meta'>, '__new__': <function wrap at 0x2743140>, '__init__': <function wrap at 0x27438c0>}) {}
 <function __init__ at 0x27432a8>  () ->  None
creating instance
 <function __call__ at 0x2743230> (<class '__main__.Type'>,) {}
        <function __new__ at 0x27431b8> (<class '__main__.Type'>, <class '__main__.Type'>) {}
        <function __new__ at 0x27431b8>  () ->  <__main__.Type object at 0x2745590>
        <function __init__ at 0x2743050> (<__main__.Type object at 0x2745590>, <class '__main__.Type'>) {}
        <function __init__ at 0x2743050>  () ->  None
 <function __call__ at 0x2743230>  () ->  <__main__.Type object at 0x2745590>
"""