Sentry Answers>Python>

Read a file line by line into a list Python

Read a file line by line into a list Python

David Y.

The ProblemJump To Solution

In Python, how do I read a file and store each line in a list?

The Solution

We can read the lines of a file into a list by opening the file and looping through it using a list comprehension:

Click to Copy
with open('myfile.txt') as f: lines = [line.rstrip() for line in f]

The with syntax ensures that the file will be closed once our list is assembled. rstrip() is a string method that removes trailing whitespace and newlines.

Note that for sufficiently large files, this operation could become slow and memory intensive, and, depending on the purpose of our script, it may be more efficient to apply a function to each line as it’s read in rather than storing each line in a list for later manipulation. For example:

Click to Copy
with open('myfile.txt') as f: for line in f: process(line) def process(line): # insert line processing code here
  • Sentry BlogPython Performance Testing: A Comprehensive Guide
  • Sentry BlogLogging in Python: A Developer’s Guide
  • logo
    Listen to the Syntax Podcast

    Tasty Treats for Web Developers brought to you by Sentry. Web development tips and tricks hosted by Wes Bos and Scott Tolinski

    Listen to Syntax

Loved by over 4 million developers and more than 90,000 organizations worldwide, Sentry provides code-level observability to many of the world’s best-known companies like Disney, Peloton, Cloudflare, Eventbrite, Slack, Supercell, and Rockstar Games. Each month we process billions of exceptions from the most popular products on the internet.

© 2024 • Sentry is a registered Trademark
of Functional Software, Inc.