def _shadowGetByName(username):
    """
    Look up a user in the /etc/shadow database using the spwd module. If it is
    not available, return L{None}.

    @param username: the username of the user to return the shadow database
        information for.
    @type username: L{str}
    """
    if spwd is not None:
        f = spwd.getspnam
    else:
        return None
    return runAsEffectiveUser(0, 0, f, username)

    Look up a user in the /etc/shadow database using the spwd module. If it is
    not available, return L{None}.

    @param username: the username of the user to return the shadow database
        information for.
    @type username: L{str}
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/checkers.py