How to read a file line-by-line into a list in Python?

To read a file line-by-line into a list in Python, you can use the following methods. Each approach handles newline characters (\n) differently, so choose based on your needs:

Method 1: Using readlines()

Reads all lines into a list including newline characters:

with open('file.txt', 'r') as file:
    lines = file.readlines()  # Includes '\n' at the end of each line

To remove newline characters:

with open('file.txt', 'r') as file:
    lines = [line.rstrip('\n') for line in file]  # Removes only the trailing '\n'
    # OR
    lines = [line.strip() for line in file]       # Removes leading/trailing whitespace and '\n'

Method 2: Iterate Directly Over the File Object

Memory-efficient and clean:

with open('file.txt', 'r') as file:
    lines = []
    for line in file:
        lines.append(line.rstrip('\n'))  # Or line.strip()

Method 3: Use read() + splitlines()

Read the entire file as a string and split into lines without newlines:

with open('file.txt', 'r') as file:
    content = file.read()
    lines = content.splitlines()  # Automatically removes '\n' and other line endings

Key Differences

Method	Includes \n?	Handles Different Line Endings?	Memory Efficiency
file.readlines()	Yes	❌ (Retains \n)	❌ (Reads all at once)
read() + splitlines()	No	✅ (Handles \n, \r\n, etc.)	❌ (Reads all at once)
Iterating line-by-line	Configurable	✅	✅ (Streams lines)

Examples

Sample File (file.txt):

Hello
World

Python

Output Comparison

1. Using readlines():

   ['Hello\n', 'World\n', '\n', 'Python']

2. Using rstrip('\n'):

   ['Hello', 'World', '', 'Python']

3. Using splitlines():

   ['Hello', 'World', '', 'Python']

Edge Cases

• Empty Lines: Preserved as empty strings ('').
• Trailing Newlines: Use rstrip('\n') to avoid stripping other whitespace.
• Large Files: For huge files, iterate line-by-line (Method 2) to avoid loading the entire file into memory.

Final Recommendation

Use splitlines() for simplicity and automatic handling of line endings:

with open('file.txt', 'r') as file:
    lines = file.read().splitlines()

Or for memory efficiency with large files:

with open('file.txt', 'r') as file:
    lines = [line.rstrip('\n') for line in file]