Why the second time I run "readlines" on the same file nothing is returned?

Question

>>> f = open('/tmp/version.txt', 'r')
>>> f
<open file '/tmp/version.txt', mode 'r' at 0xb788e2e0>
>>> f.readlines()
['2.3.4\n']
>>> f.readlines()
[]
>>>

I've tried this in Python's interpreter. Why does this happen?

Answer 1

You need to seek to the beginning of the file. Use f.seek(0) to return to the begining:

>>> f = open('/tmp/version.txt', 'r')
>>> f
<open file '/tmp/version.txt', mode 'r' at 0xb788e2e0>
>>> f.readlines()
['2.3.4\n']
>>> f.seek(0)
>>> f.readlines()
['2.3.4\n']
>>>

Answer 2

Python keeps track of where you are in the file. When you're at the end, it doesn't automatically roll back over. Try f.seek(0).