1224作业

1.创建一个文件，文件的第一行写入0，再创建20个任务线程，他们同时打开文件并将文件第一行读出来，加1写回去（将文件原有值覆盖掉）请保证20个任务线程完成后，文件中的第一行一定是20！

from threading import Thread

with open('test', mode='w') as f:
    f.write('0')

def cre_thr():
    with open('test', mode='r') as e:
        a = int(e.read())
        print(a)
        a += 1
    with open('test', mode='w+') as g:
        g.write(str(a))
        print(g.read())

if __name__ == '__main__':
    for i in range(20):
        thr = Thread(target=cre_thr)
        thr.start()
        thr.join()