Python 在读取文本文件时，使用文件循环中的for行，如何选择前一行？

下面是一个示例代码

with open('somefile.txt', 'r') as file:
    for line in file:
        find = 'some string'
        if find in line:
            if previous line is the same as this line: #how to write this ?
                pass
            else:
                print(line)

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如何在此代码中写入第5行？

在每次迭代时保存前一行：

with open('test.txt', 'r') as file:
    previous = None
    find = 'n'
    for line in file:
        if find in line:
            if line != previous:
                print(line)
        previous = line

样本输入：

hello
no
no
hello

输出：

no  

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或者，不要回头看，而是在一行包含字符串时做一个记录，并检查下一行是否也包含字符串。