readlines() method of File Object in Python

Question

I have a quick question about the readlines() method for file objects in Python.

I have a file (file1.txt) containing the following:

one
two
three
four
five

I know I can use readlines() on this file in the interpreter like so:

>>>f = open('file1.txt', 'r+')
>>>f.readlines()
['one\n', 'two\n', 'three\n', 'four\n', 'five\n']

Similarly, I can do this:

>>>f = open('file1.txt', 'r+')
>>>lines = f.readlines()
>>>lines
['one\n', 'two\n', 'three\n', 'four\n', 'five\n']

However, it seems like I can only run the readlines() method once:

>>>f = open('file1.txt', 'r+')
>>>f.readlines()
['one\n', 'two\n', 'three\n', 'four\n', 'five\n']
>>>lines = f.readlines()
>>>lines
[]

What is going on here? Why does f.readlines() return an empty list the second time I call it?

Thanks.

You also can only run`f.read()` once unless you run `f.seek(0)`. This maybe is a dupe. Let me search about it. — Remi Guan, Dec 13 '15 at 07:33
http://stackoverflow.com/questions/3906137/why-cant-i-call-read-twice-on-an-open-file — pvg, Dec 13 '15 at 07:33
Thanks for pointing me to the first question asking this. My google skills are apparently lacking. — detroitwilly, Dec 13 '15 at 16:37

score 1 · Answer 1 · answered Dec 13 '15 at 07:34

1

When you read the file once, the file pointer have moved to the end of the file, you have to call f.seek(0) to move the file pointer back to the start.

answered Dec 13 '15 at 07:34

shellfly

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readlines() method of File Object in Python

1 Answers1