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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 schemes(self):
 """Return supported schemes."""

        if not self._schemes:
            _schemes = []
            if self.types.keys() & _HTTP_PROTOS:
                _schemes.append('HTTP')
            if self.types.keys() & _HTTPS_PROTOS:
                _schemes.append('HTTPS')
            self._schemes = tuple(_schemes)
        return self._schemes