File Handling

Use open() to work with files. Prefer the with statement (context manager) so the file is automatically closed even if an error occurs.

with open("file.txt", "mode") as f:
    # Read or write to the file

Modes

Mode	Meaning
r	Read (default), file must exist
w	Write, truncates/creates the file
a	Append, writes to the end, creates if missing
x	Create, fails if the file already exists
r+	Read and write
b	Binary mode (e.g. rb, wb)

Reading

with open("file.txt") as f:
    content = f.read()          # Entire file as one string

with open("file.txt") as f:
    lines = f.readlines()       # List of lines (keeps "\n")

# Iterate line by line (memory friendly for large files)
with open("file.txt") as f:
    for line in f:
        print(line.rstrip())    # Strip trailing newline

Writing / Appending

with open("file.txt", "w") as f:
    f.write("first line\n")     # Overwrites existing content
    f.writelines(["a\n", "b\n"])

with open("file.txt", "a") as f:
    f.write("appended line\n")  # Adds to the end

Working with paths (pathlib is the modern approach)

from pathlib import Path

path = Path("data") / "file.txt"
text = path.read_text()         # Read whole file
path.write_text("hello")        # Write whole file
print(path.exists())            # True / False