diy.py

new_data=''
with open(r'C:\Users\ASUS\Desktop\book.txt','r',encoding='utf-8')as filel:
    for data in filrl:
        if '小强：10本'in data:
            data=data.replace('小强：10本','小强：11本)
        if '小兰： 12本'in data:
            data=data.replace('小兰：12本','小兰：14本)
        new_data +=data

with open(r'C:\Users\ASUS\Desktop\book.txt','w',encoding='utf-8')as filel:
    filel.write(new_data)

with open(r'C:\Users\ASUS\Desktop\book.txt','r',encoding='utf-8')as filel:
    a=filel.read()
    print(a)