def define_treatment_wells(exclude_outer=1, plate_dims=[16, 24]):
    """Defines set of inner wells to be used for treatments

    Parameters
    ----------
    exclude_outer : int
       defines outer well columns and rows to to exclude
    plate_dims : list of int
    
    Returns
    -------
    tr_wells, list(set(exclude_wells)): tuple of lists
       lists of treatment wells and outer wells
    """
    cols = ["%02d" % s for s in range(1, plate_dims[1]+1)]
    rows = [chr(65+n) for n in range(plate_dims[0])]
    if exclude_outer:
        rows = rows[exclude_outer:-exclude_outer]
        cols = cols[exclude_outer:-exclude_outer]
    tr_wells = []
    for row in rows:
        for col in cols:
            tr_wells.append("%s%s" % (row, col))
    return tr_wells