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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 _ensure_unicode_string(string):
 """Returns a unicode string for string. :param string: The input string. :type string: `basestring` :returns: A unicode string. :rtype: `unicode` """

        if not isinstance(string, six.text_type):
            string = string.decode('utf-8')
        return string