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Viewing changes to Epsilon/epsilon/remember.py

  • Committer: Jean-Paul Calderone
  • Date: 2014-06-29 20:33:04 UTC
  • mfrom: (2749.1.1 remove-epsilon-1325289)
  • Revision ID: exarkun@twistedmatrix.com-20140629203304-gdkmbwl1suei4m97
merge lp:~exarkun/divmod.org/remove-epsilon-1325289

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Epsilon/epsilon/remember.py
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# -*- test-case-name: epsilon.test.test_remember -*-
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"""
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This module implements a utility for managing the lifecycle of attributes
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related to a particular object.
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"""
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from epsilon.structlike import record
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class remembered(record('creationFunction')):
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    """
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    This descriptor decorator is applied to a function to create an attribute
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    which will be created on-demand, but remembered for the lifetime of the
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    instance to which it is attached.  Subsequent accesses of the attribute
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    will return the remembered value.
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    @ivar creationFunction: the decorated function, to be called to create the
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        value.  This should be a 1-argument callable, that takes only a 'self'
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        parameter, like a method.
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    """
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    value = None
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    def __get__(self, oself, type):
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        """
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        Retrieve the value if already cached, otherwise, call the
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        C{creationFunction} to create it.
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        """
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        remembername = "_remembered_" + self.creationFunction.func_name
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        rememberedval = oself.__dict__.get(remembername, None)
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        if rememberedval is not None:
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            return rememberedval
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        rememberme = self.creationFunction(oself)
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        oself.__dict__[remembername] = rememberme
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        return rememberme
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__all__ = ['remembered']