// SYSTEM PANEL //
[ROOT]
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usr
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lib64
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python2.7
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Demo
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newmetaclasses
[ PARENT ]
EDIT :: Eiffel.py
"""Support Eiffel-style preconditions and postconditions.""" from types import FunctionType as function class EiffelBaseMetaClass(type): def __new__(meta, name, bases, dict): meta.convert_methods(dict) return super(EiffelBaseMetaClass, meta).__new__(meta, name, bases, dict) @classmethod def convert_methods(cls, dict): """Replace functions in dict with EiffelMethod wrappers. The dict is modified in place. If a method ends in _pre or _post, it is removed from the dict regardless of whether there is a corresponding method. """ # find methods with pre or post conditions methods = [] for k, v in dict.iteritems(): if k.endswith('_pre') or k.endswith('_post'): assert isinstance(v, function) elif isinstance(v, function): methods.append(k) for m in methods: pre = dict.get("%s_pre" % m) post = dict.get("%s_post" % m) if pre or post: dict[m] = cls.make_eiffel_method(dict[m], pre, post) class EiffelMetaClass1(EiffelBaseMetaClass): # an implementation of the "eiffel" meta class that uses nested functions @staticmethod def make_eiffel_method(func, pre, post): def method(self, *args, **kwargs): if pre: pre(self, *args, **kwargs) x = func(self, *args, **kwargs) if post: post(self, x, *args, **kwargs) return x if func.__doc__: method.__doc__ = func.__doc__ return method class EiffelMethodWrapper: def __init__(self, inst, descr): self._inst = inst self._descr = descr def __call__(self, *args, **kwargs): return self._descr.callmethod(self._inst, args, kwargs) class EiffelDescriptor(object): def __init__(self, func, pre, post): self._func = func self._pre = pre self._post = post self.__name__ = func.__name__ self.__doc__ = func.__doc__ def __get__(self, obj, cls): return EiffelMethodWrapper(obj, self) def callmethod(self, inst, args, kwargs): if self._pre: self._pre(inst, *args, **kwargs) x = self._func(inst, *args, **kwargs) if self._post: self._post(inst, x, *args, **kwargs) return x class EiffelMetaClass2(EiffelBaseMetaClass): # an implementation of the "eiffel" meta class that uses descriptors make_eiffel_method = EiffelDescriptor def _test(metaclass): class Eiffel: __metaclass__ = metaclass class Test(Eiffel): def m(self, arg): """Make it a little larger""" return arg + 1 def m2(self, arg): """Make it a little larger""" return arg + 1 def m2_pre(self, arg): assert arg > 0 def m2_post(self, result, arg): assert result > arg class Sub(Test): def m2(self, arg): return arg**2 def m2_post(self, Result, arg): super(Sub, self).m2_post(Result, arg) assert Result < 100 t = Test() t.m(1) t.m2(1) try: t.m2(0) except AssertionError: pass else: assert False s = Sub() try: s.m2(1) except AssertionError: pass # result == arg else: assert False try: s.m2(10) except AssertionError: pass # result == 100 else: assert False s.m2(5) if __name__ == "__main__": _test(EiffelMetaClass1) _test(EiffelMetaClass2)
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