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76 lines
1.9 KiB
76 lines
1.9 KiB
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class Patch(object):
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"""
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Implements a class decorator suitable for patching an existing class with
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a new namespace.
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For example, consider this trivial class (that your code doesn't own):
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>>> class MyClass:
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... def __init__(self, param):
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... self.param = param
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... def bar(self):
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... print("orig bar")
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To add attributes to MyClass, you can use Patch:
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>>> @Patch(MyClass)
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... class JustANamespace:
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... def print_param(self):
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... print(self.param)
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>>> ob = MyClass('foo')
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>>> ob.print_param()
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foo
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The namespace is assigned None, so there's no mistaking the purpose
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>>> JustANamespace
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The patcher will replace the existing methods:
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>>> @Patch(MyClass)
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... class SomeNamespace:
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... def bar(self):
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... print("replaced bar")
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>>> ob = MyClass('foo')
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>>> ob.bar()
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replaced bar
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But it will not replace methods if no_replace is indicated.
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>>> @Patch(MyClass)
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... class AnotherNamespace:
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... @no_replace
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... def bar(self):
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... print("candy bar")
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>>> ob = MyClass('foo')
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>>> ob.bar()
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replaced bar
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"""
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def __init__(self, target):
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self.target = target
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def __call__(self, patches):
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for name, value in list(vars(patches).items()):
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if name in vars(ReferenceEmptyClass):
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continue
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no_replace = getattr(value, '__no_replace', False)
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if no_replace and hasattr(self.target, name):
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continue
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setattr(self.target, name, value)
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def no_replace(f):
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"""
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Method decorator to indicate that a method definition shall
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silently be ignored if it already exists in the target class.
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"""
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f.__no_replace = True
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return f
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class ReferenceEmptyClass(object):
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"""
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This empty class will serve as a reference for attributes present on
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any class.
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"""
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