I'm trying to do something like this

Lines = file.readlines()

# do something

Lines = file.readlines()

but the second time Lines is empty. Is that normal?

解決方案

Yes, because .readlines() advances the file pointer to the end of the file.

Why not just store a copy of the lines in a variable?

file_lines = file.readlines()

Lines = list(file_lines)

# do something that modifies Lines

Lines = list(file_lines)

It'd be far more efficient than hitting the disk twice. (Note that the list() call is necessary to create a copy of the list so that modifications to Lines won't affect file_lines.)

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