Returns a unicode string for string.

        :param string:
            The input string.
        :type string:
            `basestring`

        :returns:
            A unicode string.
        :rtype:
            `unicode`

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