diy.py

# 写入同学们的捐赠明细：'小兰：12本'、'小丽：11本'、'李文：9'
url=r'c:\Users\ryc66\OneDrive - 6699e5\Desktop\1.txt'
# file=open(url,"w",encoding="utf-8")
# file.write('小兰：12本\n')
# file.write('小丽：11本\n')
# file.write('李文：9本')
# file.close()
# file=open(url,"a",encoding="utf-8")
# file.write('小明：10本\n')
# file.close()
# with open(url,"a",encoding="utf-8") as file:
#     file.write('小红：13本\n')
new=""
with open(url,"w+",encoding="utf-8") as file:
    for i in file:
        if '李文：9本' in i:
            i=i.replace('李文：9本','李文：10本')
        new+=i
# print(new)        
# with open(url,"w",encoding="utf-8") as file:
    file.write(new)