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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_token(self, oauth_request, token_type='access'):
 """Try to find the token for the provided request token key."""

        token_field = oauth_request.get_parameter('oauth_token')
        token = self.data_store.lookup_token(token_type, token_field)
        if not token:
            raise OAuthError('Invalid %s token: %s' % (token_type, token_field))
        return token