def _check_writable_fields(row):
    """Check no potentially conflicting fields for a writing action."""
    keys = row.keys()

    # XXX: instead of preventing use of end_date/end_time and length in the
    # same input, use successively complex conflict resolution plans:
    #
    # 1. allow it as long as they don't conflict by row
    # 2. conflict resolution by option
    # 3. conflict resolution interactively

    if 'length' in keys and ('end_date' in keys or 'end_time' in keys):
        raise NotImplementedError
Check no potentially conflicting fields for a writing action.
gcalcli/actions.py