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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 add_passthru(self, prefix):
 """ Register a URL prefix to passthru any non-matching mock requests to. For example, to allow any request to 'https://example.com', but require mocks for the remainder, you would add the prefix as so: """

        if _has_unicode(prefix):
            prefix = _clean_unicode(prefix)
        self.passthru_prefixes += (prefix,)