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"""An example of a descriptor with a ``__delete__()`` method.
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The code is for illustration purposes only, and it does not correspond to any
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actual implementation.
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"""
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class ProtectedAttribute:
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"""A class attribute that can be protected against deletion"""
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def __set_name__(self, owner, name):
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self.name = name
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def __set__(self, instance, value):
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instance.__dict__[self.name] = value
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def __delete__(self, instance):
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raise AttributeError(f"Can't delete {self.name} for {instance!s}")
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class ProtectedUser:
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"""
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>>> usr = ProtectedUser('jsmith', '127.0.0.1')
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>>> usr.username
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'jsmith'
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>>> del usr.username
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Traceback (most recent call last):
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...
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AttributeError: Can't delete username for ProtectedUser[jsmith]
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>>> usr.location
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'127.0.0.1'
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>>> del usr.location
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>>> usr.location
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Traceback (most recent call last):
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...
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AttributeError: 'ProtectedUser' object has no attribute 'location'
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"""
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username = ProtectedAttribute()
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def __init__(self, username, location):
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self.username = username
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self.location = location
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def __str__(self):
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return f"{self.__class__.__name__}[{self.username}]"
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if __name__ == '__main__':
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import doctest
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doctest.testmod()
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