Using the __call__ method of a metaclass instead of __new__?

Question

When discussing metaclasses, the docs state:

You can of course also override other class methods (or add new methods); for example defining a custom

Answer 1

It's a matter of lifecycle phases and what you have access to. __call__ gets called after __new__ and is passed the initialization parameters before they get passed on to __init__, so you can manipulate them. Try this code and study its output:

class Meta(type):
    def __new__(cls, name, bases, newattrs):
        print "new: %r %r %r %r" % (cls, name, bases, newattrs,)
        return super(Meta, cls).__new__(cls, name, bases, newattrs)

    def __call__(self, *args, **kw):
        print "call: %r %r %r" % (self, args, kw)
        return super(Meta, self).__call__(*args, **kw)

class Foo:
    __metaclass__ = Meta

    def __init__(self, *args, **kw):
        print "init: %r %r %r" % (self, args, kw)

f = Foo('bar')
print "main: %r" % f