python中readlines,在python中连续两次使用readlines -尊龙游戏旗舰厅官网

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?

尊龙游戏旗舰厅官网的解决方案

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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