Locating files reliably.
THE PROBLEM
Paths written for one system fail on another.
WHAT TO USE
Python's path handling, rather than joining strings manually.
WHY
It handles separators correctly on every platform.
ABSOLUTE AND RELATIVE PATHS
Absolute paths start from the root and always mean the same thing.
Relative paths depend on where the program was run from.
WHAT THAT CAUSES
A script working when run from its own folder and failing from elsewhere.
WHAT TO DO ABOUT IT
Build paths relative to the script's own location, not the current directory.
WHAT TO CHECK
Whether a path exists Whether it is a file or a directory
WHAT TO BE CAREFUL WITH
Paths from user input, which can point anywhere Creating directories that already exist Assuming a path separator
THE USER INPUT POINT
Never use a path supplied from outside without validating it.
That is how files outside the intended directory get read or written.
WHAT TO USE FOR TEMPORARY FILES
The facilities provided for them, which handle cleanup.
