syntax.py

# -*- coding: utf-8 -*-
"""
    the test case is valid under python3
"""

def test_type_func():
    """test 'type' function, to create a class by type()"""
    class A(object):
        def echo_a(self):
            print("echo A")

    def echo_my_class(self):
            print("echo MyClass")

    my_class = type('my_class', (A, ), {'echo_my_class':echo_my_class})

    obj = my_class()
    print(my_class.__mro__)
    print(my_class.mro())
    obj.echo_a()
    obj.echo_my_class()


def test_class():
    class Base:
        pass

    class A(Base):
        def __init__(self, x):
            super().__init__()
            print('print A.__init__()', x)

    class B(A):
        def __init__(self):
            print('print B.__init__')
            super().__init__("input x")

    obj = B()
    print(obj)


def meta_func(name, bases, attrs):
    """allocate memory operation"""
    print("enter MyMetaClass.__new__()")
    set_attrs = ((name, value) for name, value in attrs.items() if not name.startswith('__'))
    uppercase_attr = dict((name.upper(), value) for name, value in set_attrs)
    return type(name, bases, uppercase_attr)


class MyMetaClass(type):
    def __new__(mcs, name, bases, attrs):
        """allocate memory operation"""
        print("enter MyMetaClass.__new__()")
        if name == "Model":
            return super().__new__(mcs, name, bases, attrs)
        else:
            set_attrs = ((name, value) for name, value in attrs.items() if not name.startswith('__'))
            uppercase_attr = dict((name.upper(), value) for name, value in set_attrs)
            return super().__new__(mcs, name, bases, uppercase_attr)

    def __init__(cls, name, bases, attrs):
        """enter MyMetaClass.__init__()"""
        print("enter MyMetaClass.__init__()")
        super().__init__(name,bases,attrs)
        cls.__instance = None

    def __call__(cls, *args, **kargs):
        """enter MyMetaClass.__call__()"""
        print("enter MyMetaClass.__call__()")
        if cls.__instance:
            return cls.__instance
        else:
            cls._instance = super().__call__(*args, **kargs)
            return cls.__instance


class Earth(metaclass=MyMetaClass):
    People = "abc"
    __instance = None

    def __init__(self):
        self.AAA = 1
        print("enter Earth.__init__() ...")


def test_meta_class():
    """ test __metaclass__ __new__ __init__ __call__ """
    earth1 = Earth()
    earth2 = Earth()
    print(id(earth1), id(earth2))


def __main():
    print("[TEST] type .....................")
    test_type_func()
    print("[END] ...........................")
    print("[TEST] class ....................")
    test_class()
    print("[END] ...........................")
    print("[TEST] meta class ...............")
    test_meta_class()
    print("[END] ...........................")


if __name__ == '__main__':
    __main()