as :class:`dateutil.tz.tzutc`.

:param dt_str:
    A string or stream containing only an ISO-8601 datetime string

:return:
    Returns a :class:`datetime.datetime` representing the string.
    Unspecified components default to their lowest value.

.. warning::

    As of version 2.7.0, the strictness of the parser should not be
    considered a stable part of the contract. Any valid ISO-8601 string
    that parses correctly with the default settings will continue to
    parse correctly in future versions, but invalid strings that
    currently fail (e.g. ``2017-01-01T00:00+00:00:00``) are not
    guaranteed to continue failing in future versions if they encode
    a valid date.

.. versionadded:: 2.7.0
Nr*