cpython/Demo/metaclasses/Simple.py

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import types
class Tracing:
def __init__(self, name, bases, namespace):
"""Create a new class."""
self.__name__ = name
self.__bases__ = bases
self.__namespace__ = namespace
def __call__(self):
"""Create a new instance."""
return Instance(self)
class Instance:
def __init__(self, klass):
self.__klass__ = klass
def __getattr__(self, name):
try:
value = self.__klass__.__namespace__[name]
except KeyError:
raise AttributeError(name)
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if type(value) is not types.FunctionType:
return value
return BoundMethod(value, self)
class BoundMethod:
def __init__(self, function, instance):
self.function = function
self.instance = instance
def __call__(self, *args):
print("calling", self.function, "for", self.instance, "with", args)
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return self.function(self.instance, *args)
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Trace = Tracing('Trace', (), {})
class MyTracedClass(Trace):
def method1(self, a):
self.a = a
def method2(self):
return self.a
aninstance = MyTracedClass()
aninstance.method1(10)
print(aninstance.method2())