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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_signature_method(self, request):
 """Figure out the signature with some defaults."""

        signature_method = request.get('oauth_signature_method')
        if signature_method is None:
            signature_method = SIGNATURE_METHOD

        try:
            # Get the signature method object.
            return self.signature_methods[signature_method]
        except KeyError:
            signature_method_names = ', '.join(self.signature_methods.keys())
            raise Error('Signature method %s not supported try one of the '
                        'following: %s'
                            % (signature_method, signature_method_names))