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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 get_sid(principal):
    '''
    Converts a username to a sid, or verifies a sid. Required for working with
    the DACL.

    Args:

        principal(str):
            The principal to lookup the sid. Can be a sid or a username.

    Returns:
        PySID Object: A sid

    Usage:

    .. code-block:: python

        # Get a user's sid
        salt.utils.win_dacl.get_sid('jsnuffy')

        # Verify that the sid is valid
        salt.utils.win_dacl.get_sid('S-1-5-32-544')
    '''
    # If None is passed, use the Universal Well-known SID "Null SID"
    if principal is None:
        principal = 'NULL SID'

    # Test if the user passed a sid or a name
    try:
        sid = salt.utils.win_functions.get_sid_from_name(principal)
    except CommandExecutionError:
        sid = principal

    # Test if the SID is valid
    try:
        sid = win32security.ConvertStringSidToSid(sid)
    except pywintypes.error:
        log.exception('Invalid user/group or sid: %s', principal)
        raise CommandExecutionError(
            'Invalid user/group or sid: {0}'.format(principal))
    except TypeError:
        raise CommandExecutionError

    return sid