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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 set_key_startswith(self, key_startswith):
 """ Set key startswith policy condition. :param key_startswith: set key prefix name. """

        is_non_empty_string(key_startswith)

        self.policies.append(('starts-with', '$key', key_startswith))
        self.form_data['key'] = key_startswith