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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 _is_utf_8(txt):
 """ Check a string is utf-8 encoded :param bytes txt: utf-8 string :return: Whether the string\ is utf-8 encoded or not :rtype: bool """

    assert isinstance(txt, six.binary_type)

    try:
        _ = six.text_type(txt, 'utf-8')
    except (TypeError, UnicodeEncodeError):
        return False
    else:
        return True