仅在文本文件的第一行中替换某些元素 [英] Replace certain element in only first line of the text file

问题描述

我有一个文本文件，想替换某些元素"NaN".

I have a text file and would like to replace certain elements which is "NaN".

我通常使用file.replace函数在整个文本文件中更改具有一定数量的NaN.
现在，我只想在文本文件的第一行而不是整个文本中用一定数量的NaN代替.
您能给我提示这个问题吗?

I usually have used file.replace function for change NaNs with a certain number through entire text file.
Now, I would like to replace NaNs with a certain number in only first line of text file, not whole text.
Would you give me a hint for this problem?

推荐答案

您只能读取整个文件，在第一行调用.replace()并将其写入新文件.

You can only read the whole file, call .replace() for the first line and write it to the new file.

with open('in.txt') as fin:
    lines = fin.readlines()
lines[0] = lines[0].replace('old_value', 'new_value')

with open('out.txt', 'w') as fout:
    for line in lines:
        fout.write(line)

如果文件不是很大，则可以只使用.join():

If your file isn't really big, you can use just .join():

with open('out.txt', 'w') as fout:
    fout.write(''.join(lines))

如果它真的很大，您最好同时读取和写入行.

And if it is really big, you would probably better read and write lines simultaneously.

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