Read file line by line in Python

Reading a file line by line in Python is a common task when dealing with text files, logs, or large datasets.
It’s efficient, memory-friendly, and allows you to process each line individually without loading the entire file into memory.

In this article, you’ll learn multiple ways to read files line by line in Python, including examples using for loops, readline(), readlines(), and context managers.

Method 1: Using a for Loop (Best & Pythonic Way)

# Open file and iterate line by line
with open('sample.txt', 'r') as file:
for line in file: print(line.strip())

Output:

 Line 1: Hello World Line 2: Python is awesome Line 3: File handling made easy 

Why use this?
> Most Pythonic and efficient method
> Automatically handles large files (reads line by line)
> Closes the file automatically using with statement

Method 2: Using readline() in a Loop

readline() reads one line at a time. This gives you fine-grained control over how each line is processed.

file = open('sample.txt', 'r')

file.close()


Output:

 Line 1: Hello World Line 2: Python is awesome Line 3: File handling made easy 

Method 3: Using readlines() (For Smaller Files)

readlines() reads all lines into a list — not memory-efficient for very large files, but simple for small ones.


with open('sample.txt', 'r') as file:
lines = file.readlines()

for line in lines:
print(line.strip())


Output:

 Line 1: Hello World Line 2: Python is awesome Line 3: File handling made easy 

Method 4: Using enumerate() to Track Line Numbers

You can easily print line numbers while reading a file.


with open('sample.txt', 'r') as file:
for line_number, line in enumerate(file, start=1):
print(f"Line {line_number}: {line.strip()}")

Output:

 Line 1: Hello World Line 2: Python is awesome Line 3: File handling made easy 

Method 5: Read File Lines into a List Using List Comprehension

with open('sample.txt', 'r') as file:
lines = [line.strip() for line in file]

print(lines)


Output:

['Line 1: Hello World', 'Line 2: Python is awesome', 'Line 3: File handling made easy']

Method 6: Using fileinput Module (Advanced)

The fileinput module is great when you want to read from multiple files seamlessly.

import fileinput

for line in fileinput.input(files=('sample.txt', 'log.txt')):
print(line.strip())


Output:

 Line 1: Hello World Line 2: Python is awesome Line 3: File handling made easy ... 

Why use this?
> Reads multiple files as if they were a single stream
> Excellent for merging or analyzing log files

Method 7: Handling Large Files Efficiently

For very large files, use generators or buffered reading to reduce memory usage.


def read_large_file(file_path):
with open(file_path, 'r') as f:
for line in f:
yield line.strip()

for line in read_large_file('large_dataset.txt'):
print(line)


Output:

Prints each line without loading the entire file into memory.

Why use this?
> Extremely memory-efficient
> Perfect for reading multi-GB log or dataset files

Read Lines and Skip Empty or Comment Lines


with open('config.txt', 'r') as file:
for line in file: stripped = line.strip() if stripped and not stripped.startswith('#'): print(stripped)

Output:

Prints only non-empty, non-comment lines.

Why use this?
> Useful for reading config or code files
> Skips blank lines and comments automatically.

with open('data.txt', 'r') as f:
    for line in f:
        print(line.strip())

f = open('data.txt', 'r')
line = f.readline()
while line:
    print(line.strip())
    line = f.readline()
f.close()

with open('data.txt', 'r') as f:
    lines = f.readlines()
print(lines)

with open('large_file.txt', 'r') as f:
    for line in f:
        process(line)

with open('data.txt', 'r') as f:
    for line in f:
        print(line.strip())

with open('data.txt', 'r') as f:
    for i, line in enumerate(f, start=1):
        print(f"Line {i}: {line.strip()}")

from pathlib import Path

lines = Path('data.txt').read_text().splitlines()
for line in lines:
    print(line)

with open('data.txt', 'r') as f:
    lines = f.readlines()

print(lines[0])      # First line
print(lines[2:5])    # Lines 3 to 5

with open('data.txt', 'r', encoding='utf-8', errors='ignore') as f:
    for line in f:
        print(line)