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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_version_mode(self, mode=None):
 """Return a VersionMode for a mode name. When the mode is None, we are working with the 'base' mode. """

        version_mode = self._version_modes.get(mode)
        if not version_mode:
            version_mode = self._version_modes[mode] = VersionMode(name=mode)
        return version_mode