python中yield使用

 excel数据有上千条，最好不要一次性全部读出来放在列表会消耗内存，需要每读一条用yield返回一条；当运行到yield '';的时候,程序暂停了,不会往下继续执行,

 

class SDMS(object):

    def cpyExcel(self, path):
        if os.path.isfile(path):
            print("%s文件存在" % path)
        else:
            print("%s文件不存在" % path)
            return
    
        def readExcel(path):
            xls = rpa.excel.open(path)
            sheet = xls.get_sheet()
            col_num = int(sheet.col_count())
            for i in range(1, col_num + 1):
                col_letter = get_column_letter(i)
                print(sheet.read(col_letter))
                yield (sheet.read(col_letter))
            xls.close()
    
        return readExcel(path)
    
    
    def writeCpyExcel(self, path, data_it):
        col_num = 1
        col_letter = get_column_letter(col_num)
        xls = rpa.excel.create()
        sheet = xls.get_sheet()
        while True:
            try:
                sheet.write(col_letter, next(data_it))
                col_num += 1
                col_letter = get_column_letter(col_num)
            except:
                print("except, 数据读取完成。")
                break
        xls.save(file=path)
        xls.close()

def start():
    sdms = SDMS()
    sync_filename = time.strftime("%Y%m%d_%H%M%S", time.localtime()) + "同步数据.xlsx"
    sync_filepath = os.path.join(logdir, sync_filename)
    data_it = sdms.cpyExcel(self.filepath)   #读取excel返回迭代器data_it，因为原本的excel无法编辑，所以要复制出来编辑
    sdms.writeCpyExcel(sync_filepath, data_it) #通过迭代器data_it，再写入另外一个excel