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Groups > comp.lang.python > #43337

Re: name lookup failure using metaclasses with unittests

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On 11 April 2013 07:43, Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> wrote:

> The second question that came up was if there is a way to keep a metaclass
> defined inside the class or if the only way is to provide it externally.

Yes, using metaclasses!  I wouldn't recommend it though.  Here's a
proof of concept:

class MyType(type):
    def __new__(meta, name, bases, attrs):
        try:
            metaclass = attrs.pop('__metaclass__')
        except KeyError:
            return type.__new__(meta, name, bases, attrs)
        else:
            return metaclass(name, bases, attrs)

class MyObject(metaclass=MyType):
    pass


>>> class Test(MyObject):
...     def __metaclass__(name, bases, attrs):
...         print("Test metaclass")
...         return MyType(name, bases, attrs)
...
Test metaclass

-- 
Arnaud

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name lookup failure using metaclasses with unittests Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2013-04-10 10:18 +0200
  Re: name lookup failure using metaclasses with unittests Peter Otten <__peter__@web.de> - 2013-04-10 11:52 +0200
    Re: name lookup failure using metaclasses with unittests Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2013-04-11 09:09 +0200
    Re: name lookup failure using metaclasses with unittests Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2013-04-11 08:43 +0200
      Re: name lookup failure using metaclasses with unittests Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-11 08:19 +0000
        Re: name lookup failure using metaclasses with unittests Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2013-04-12 09:17 +0200
          Re: name lookup failure using metaclasses with unittests Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-12 10:58 -0400
      Re: name lookup failure using metaclasses with unittests Arnaud Delobelle <arnodel@gmail.com> - 2013-04-11 09:19 +0100

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