File paths with pathlib

What it is

pathlib.Path wraps file system paths: / joins segments, .name, .stem, .suffix and .parent decompose them, .read_text(), .write_bytes(), .iterdir() and .glob() perform I/O, and .resolve() returns an absolute path with symlinks resolved. PurePath variants do the same without touching the file system.

Why it matters

String concatenation of paths breaks on separators, double slashes and platform differences, and hides traversal bugs. Path objects make intent visible and provide the operations needed to keep user-supplied names inside an allowed directory.

How to apply

• Build paths with /, never with + or f-strings.
• To confine a user-supplied name to a base directory: target = (base / name).resolve() and check target.is_relative_to(base.resolve()) before use; reject names containing separators up front.
• Use with path.open() as f for streaming reads; read_text for small files.
• Prefer Path.home() and tempfile over hard-coded locations.

Pitfalls

resolve() follows symlinks, which may point outside the base; check after resolving. Comparing paths as strings ignores normalisation; compare Path objects or resolved forms. Windows and POSIX differ in case sensitivity and separators; test on both if both are supported.