往磁盘一文件st.txt里写入一字符串"012345678",并读出来，将每个数据加一后，再写入此文本文件中的第二行。

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往磁盘一文件中写入一字符串。病毒出来将每个数据加一后再写入指文本文件中的第二行。

dirname=r'C:\Users\Administrator\Desktop'

with open(dirname + "/st.txt", 'w+', encoding = 'utf-8') as f:
    f.write('012345678')
    f.seek(0)
    res = f.readline().strip()
    l =''.join( map(lambda x: str(int(x) + 1), res))
    f.write('\n' + l)

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with open('st.txt','w') as file:
    file.write('012345678')

with open('st.txt','r') as file:
    num = []
    for i in range(9):
        num.append(int(file.read(1))+1)  #逐个字符读出，加1后存入列表
        
with open('st.txt','a') as file:
    file.write('\n')   #换行
    for i in range(9):
        file.write(str(num[i]))  #写入第二行

或者：

with open('st.txt','w') as file:
    file.write('012345678')

with open('st.txt','r') as file1:
    with open('st.txt','a') as file2:
        num = []
        file2.write('\n')
        for i in range(9):
            num.append(int(file1.read(1))+1)
            file2.write(str(num[i]))

你题目的解答代码如下：

s='012345678'
# 在文件st.txt里写入一字符串"012345678"
with open(r'st.txt', 'w', encoding='utf-8') as fileObj:
    fileObj.write(s+'\n')
# 重新读出来
with open(r'st.txt', 'r', encoding='utf-8') as fileObj:
    s2 = fileObj.readline()
# 每个数据加一后，再写入此文本文件中的第二行。
with open(r'st.txt', 'a+', encoding='utf-8') as fileObj:
    s3 = "".join(map(lambda x:str(int(x)+1),s2.strip()))
    fileObj.write(s3+'\n')

# 重新读出来看看结果
with open(r'st.txt', 'r', encoding='utf-8') as fileObj:
    s4 = fileObj.read()
    print(s4)

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