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41 lines
963 B
Python
41 lines
963 B
Python
"""
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Construction of sentinel objects.
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Sentinel objects are used when you only care to check for object identity.
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"""
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import sys
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def sentinel(name, doc=None):
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@object.__new__ # bind a single instance to the name 'NotSpecified'
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class result(object):
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__doc__ = doc
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__slots__ = ('__weakref__',)
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def __new__(cls):
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raise TypeError("Can't construct new instances of %s" % name)
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def __repr__(self):
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return name
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def __reduce__(self):
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return name
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def __deepcopy__(self, _memo):
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return self
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def __copy__(self):
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return self
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cls = type(result)
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cls.__name__ = name
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try:
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# traverse up one frame to find the module where this is defined
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cls.__module__ = sys._getframe(1).f_globals.get(
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'__name__',
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'__main__',
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)
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except (AttributeError, ValueError):
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pass
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return result
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