code: def add_passthru(self, prefix):
          
          if _has_unicode(prefix):
              prefix = _clean_unicode(prefix)
          self.passthru_prefixes += (prefix,)
docs: 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:
  
          >>> responses.add_passthru('https://example.com')