Read data from files

Completed

Python gives you several ways to read text from a file. The best choice depends on the size of the file and what you want to do with it.

Read the entire file at once

The .read() method returns the entire file as a single string:

with open("notes.txt", "r") as file:
    contents = file.read()

print(contents)

This approach works well for small files, but for very large files it loads everything into memory at once.

Note

If the file doesn't exist, open() in read mode raises a FileNotFoundError. Be sure the file exists before you try to read it!

Read the file as a list of lines

The .readlines() method returns each line as a separate string in a list. Each string keeps the newline character (\n) at the end.

with open("notes.txt", "r") as file:
    lines = file.readlines()

for line in lines:
    print(line.strip())   # .strip() removes the trailing newline

Read one line at a time

The most memory-friendly way is to iterate over the file object directly. Python reads one line per loop:

with open("notes.txt", "r") as file:
    for line in file:
        print(line.strip())

This pattern is recommended for large files because only one line is held in memory at a time.

Choosing the right approach

If you want to...	Use...
Work with the entire file as one string	.read()
Get a list of lines you can index into	.readlines()
Process each line one at a time efficiently	for line in file