from xlrd import open_workbook
book = open_workbook(workbookName)
for sheet in book.sheets():
    for rowidx in range(sheet.nrows):
        row = sheet.row(rowidx)
        for colidx, cell in enumerate(row):
            if cell.value == "particularString" :
                print sheet.name
                print colidx
                print rowidx