LychnisA scratchpad for thoughts on my journey through life

The fun never stops!

class Object (object):
__metaclass__ = Metaclass

class Metaclass (type):
def __init__(cls, name, bases, *args, **kwargs):
type.__init__(cls, name, bases, *args, **kwargs)
cls.__new__ = staticmethod(cls.new)

abstractmethods = []
for clsname, clst in cls.__dict__.items():
if isinstance(clst, AbstractMethod):
abstractmethods.append(clsname)

abstractmethods.sort()
setattr(cls, ‘__abstractmethods__’, abstractmethods)

def new(self, cls):
if len(cls.__abstractmethods__):
raise NotImplementedError(‘Can\’t instantiate class `’ + \
cls.__name__ + ‘\’;\n’ + \
‘Abstract methods: ‘ + \
“, “.join(cls.__abstractmethods__))

return object.__new__(self)

class MyAbstractObject (Object):
foo = AbstractMethod(‘foo’)

class MyObject (MyAbstractObject):
def foo(self):
print ‘foo’

def main():
a = MyObject()
a.foo()
b = MyAbstractObject()
b.foo()

> python test.py
foo
Traceback (most recent call last):
  File "test.py", line 25, in ?
    main()
  File "test.py", line 21, in main
    b = MyAbstractObject()
  File "/home/ivo/p/python/abstract-classes/Metaclass.py", line 29, in new
    raise NotImplementedError('Can\'t instantiate class `' + \
NotImplementedError: Can't instantiate class `MyAbstractObject';
Abstract methods: foo

Tags: , code, example, programming, python by ivo
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