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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 authorize_url(self, state=''):
 """ return user authorize url """

        url = 'https://openapi.youku.com/v2/oauth2/authorize?'
        params = {
            'client_id': self.client_id,
            'response_type': 'code',
            'state': state,
            'redirect_uri': self.redirect_uri
        }
        return url + urlencode(params)