Incorrect output while reading text file in Python

Question

I need to read the first 30 lines of a file.

with open(filename) as f:
    lines = f.readlines(30)
print len(lines)

300

am I missing something?

possible duplicate of [Read first N lines of a file in python](http://stackoverflow.com/questions/1767513/read-first-n-lines-of-a-file-in-python) — Chaker, Jul 19 '15 at 00:12
I looked into that. I don't know why the code above is not working — Bob, Jul 19 '15 at 00:13
How about for a starter check out documentation on what is readlines parameter actually is https://docs.python.org/2/library/stdtypes.html?highlight=readlines#file.readlines — Andrey, Jul 19 '15 at 00:14
it reads all the lines, see what argument means: https://docs.python.org/2/library/stdtypes.html?highlight=readlines#file.readlines — m.wasowski, Jul 19 '15 at 00:14

score 3 · Accepted Answer · answered Jul 19 '15 at 00:14

3

According to https://docs.python.org/2/library/stdtypes.html#file.readlines, the 30 is not the number of lines to read. It is a buffer hint given in bytes.

answered Jul 19 '15 at 00:14

melpomene

1

This is not an answer, it is valid comment but it not solving the problem. – Andrey Jul 19 '15 at 00:14
How so? It explains why the code is not giving the expected output. – melpomene Jul 19 '15 at 00:15
I guess other answers given on the topic are wrong then. – Bob Jul 19 '15 at 00:17

score 1 · Answer 2 · answered Jul 19 '15 at 00:26

1

After reading the comments i have decided to give "answer" to the question: how to read first 30 lines from a file. Answer is: readline()

lines = []
for i in range(30):
    lines.append(f.readline())

Done.

answered Jul 19 '15 at 00:26

Laszlowaty

2 Answers2