Context manager to save/restore a name binding

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From	Ben Finney <ben+python@benfinney.id.au>
Newsgroups	comp.lang.python
Subject	Context manager to save/restore a name binding
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Date	Fri, 31 Aug 2012 12:36:29 +1000
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Howdy all,

I have written a context manager to save and restore a name binding::

    import contextlib

    @contextlib.contextmanager
    def preserve_value(namespace, name):
        """ A context manager to preserve, then restore, the specified binding.

            :param namespace: The namespace object (e.g. a class or dict)
                containing the name binding.
            :param name: The name of the binding to be preserved.
            :yield: None.

            When the context manager is entered, the current value bound to `name`
            in `namespace` is saved. When the context manager is exited, the
            binding is re-established to the saved value.

            """
        saved_value = getattr(namespace, name)
        yield
        setattr(namespace, name, saved_value)

The use case is <URL: http://stackoverflow.com/a/6811921/70157>, where
it's used like this::

    with preserve_value(sys, 'dont_write_bytecode'):
        sys.dont_write_bytecode = True
        module = imp.load_module(…)

That way, I can set ‘sys.dont_write_bytecode’ to the value I need in
this part of the code, knowing that however the code continues the
previous value of that setting will be restored to whatever it was
before I touched it.

Have I re-invented a context manager which already exists? Is there a
better way to do what ‘preserve_value’ is doing?

-- 
 \       “When a well-packaged web of lies has been sold to the masses |
  `\    over generations, the truth will seem utterly preposterous and |
_o__)                    its speaker a raving lunatic.” —Dresden James |
Ben Finney

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Context manager to save/restore a name binding Ben Finney <ben+python@benfinney.id.au> - 2012-08-31 12:36 +1000
  Re: Context manager to save/restore a name binding Peter Otten <__peter__@web.de> - 2012-08-31 08:27 +0200
    Re: Context manager to save/restore a name binding Ben Finney <ben+python@benfinney.id.au> - 2012-08-31 19:32 +1000
  Re: Context manager to save/restore a name binding Chris Withers <chris@python.org> - 2012-08-31 12:06 +0100

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