CODEWITHSUNDEEP
python
user1073865
user1073865

Reputation: 2583

using a text file in python

Im trying to take a text file and use only the first 30 lines of it in python. this is what I wrote:

text = open("myText.txt")
lines = myText.readlines(30)
print lines

for some reason I get more then 150 lines when I print? What am I doing wrong?

Upvotes: 1

Views: 195

Answers (4)

mac
mac

Reputation: 43031

If you are going to process your lines individually, an alternative could be to use a loop:

file = open('myText.txt')
for i in range(30):
    line = file.readline()
    # do stuff with line here

EDIT: some of the comments below express concern about this method assuming there are at least 30 lines in the file. If that is an issue for your application, you can check the value of line before processing. readline() will return an empty string '' once EOF has been reached:

for i in range(30):
    line = file.readline()
    if line == '':  # note that an empty line will return '\n', not ''!
        break
    index = new_index
    # do stuff with line here

Upvotes: 4

Shawn Chin
Shawn Chin

Reputation: 86844

The sizehint argument for readlines isn't what you think it is (bytes, not lines).

If you really want to use readlines, try text.readlines()[:30] instead.

Do note that this is inefficient for large files as it first creates a list containing the whole file before returning a slice of it.

A straight-forward solution would be to use readline within a loop (as shown in mac's answer).

To handle files of various sizes (more or less than 30), Andrew's answer provides a robust solution using itertools.islice(). To achieve similar results without itertools, consider:

output = [line for _, line in zip(range(30), open("yourfile.txt", "r"))]

or as a generator expression (Python >2.4):

output = (line for _, line in zip(range(30), open("yourfile.txt", "r")))
for line in output:
    # do something with line.

Upvotes: 2

Andrew Dalke
Andrew Dalke

Reputation: 15295

Use itertools.islice

import itertools

for line in itertools.islice(open("myText.txt"), 0, 30)):
    print line

Upvotes: 5

Sanjamal
Sanjamal

Reputation: 346

The argument for readlines is the size (in bytes) that you want to read in. Apparently 150+ lines is 30 bytes worth of data.

Doing it with a for loop instead will give you proper results. Unfortunately, there doesn't seem to be a better built-in function for that.

Upvotes: 0

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