def DFaddCatToSubcat(df):
    """this is for final assy schedule
    first column is main category
    second column is subcategory
    if first column is blank but 2nd isn't
    then copy string from previous col to current"""
    from pandas import DataFrame, isnull
    ind = df.index.values
    for i in range(1, len(ind)):
        if isnull(df.iat[i, 0]) and not isnull(df.iat[i, 1]):
            df.iat[i, 0] = df.iat[i - 1, 0]
    return df
