Read a file line by line in Python

A file object is iterable: a for loop over it gives you one line at a time. Python does not load the whole file into memory, so this works for files of any size.

The program

with open("tasks.txt", "w", encoding="utf-8") as f:
    f.write("Buy milk\nCall Grace\n\nFinish report\n")

with open("tasks.txt", encoding="utf-8") as f:
    for number, line in enumerate(f, start=1):
        line = line.strip()
        if not line:
            continue  # skip empty lines
        print(f"{number}. {line}")

1. Buy milk
2. Call Grace
4. Finish report

How it works

• Each line still ends with \n. Without .strip(), print() would add its own new line as well, and you would see an empty line after every task.
• .strip() also removes spaces at the start and end. Use .rstrip("\n") if you need to keep the spaces.
• An empty line in the file becomes "" after .strip(), and an empty string is false, so if not line: continue skips it.
• enumerate(f, start=1) counts the lines from 1. Line 3 is the empty one, so the numbers jump from 2 to 4. They match the real line numbers in the file, which helps when you report an error in a file.

All lines as a list

If the file is small and you want a list of lines, .read().splitlines() gives you the lines without the \n characters:

with open("tasks.txt", "w", encoding="utf-8") as f:
    f.write("Buy milk\nCall Grace\nFinish report\n")

with open("tasks.txt", encoding="utf-8") as f:
    lines = f.read().splitlines()

print(lines)

['Buy milk', 'Call Grace', 'Finish report']

Related programs: Read a file.