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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 guess_wxr_version(self, tree):
 """ We will try to guess the wxr version used to complete the wordpress xml namespace name. """

        for v in ('1.2', '1.1', '1.0'):
            try:
                tree.find('channel/{%s}wxr_version' % (WP_NS % v)).text
                return v
            except AttributeError:
                pass
        raise CommandError('Cannot resolve the wordpress namespace')