How to read a file line-by-line into a list?
How can you read a file line-by-line and store each line in a list using Python? What methods ensure efficient memory use and clean code when handling files? This guide explains simple and practical ways to achieve it.
Reading a file line-by-line into a list in Python is a common task, especially when dealing with text data like logs, CSVs, or configuration files. Python makes this process very straightforward and efficient.
The most Pythonic and memory-efficient way is using a context manager with the built-in open() function:
with open('filename.txt', 'r') as file:
lines = file.readlines()Key points:
- with statement: Ensures the file is automatically closed after you're done reading it, which is a good practice.
- readlines(): Reads the entire file line by line and stores each line as an element in a list.
If you want to avoid newline characters (
), you can use a list comprehension:
with open('filename.txt', 'r') as file:
lines = [line.strip() for line in file]Other things to keep in mind:
If the file is very large, readlines() might use too much memory. In such cases, iterate over the file directly:
lines = []
with open('filename.txt', 'r') as file:
for line in file:
lines.append(line.strip())- Always handle potential exceptions using try-except blocks, especially for file operations.