Defining a metaclass

class M(type):
    pass
 
class A(metaclass=M):
    pass

In Python 2, the syntax for defining a metaclass is different:

class A(object):
    __metaclass__ = M

Mypy also supports using six.with_metaclass() and @six.add_metaclassto define metaclass in a portable way:

import six
 
class A(six.with_metaclass(M)):
    pass
 
@six.add_metaclass(M)
class C(object):
    pass