Reading & Writing Files

The with statement

with open(...) as f: opens a file and guarantees it closes, even if an error happens inside the block.

with open("notes.txt", "w") as f:
    f.write("Hello, file!\n")

with open("notes.txt", "r") as f:
    content = f.read()
    print(content)

Reading line by line

Reading line by line keeps memory low for large files, since the file object is itself iterable.

with open("notes.txt") as f:
    for line in f:
        print(line.strip())

Context managers

with works because file objects are context managers — they define __enter__/__exit__ so setup and cleanup happen automatically.