psf--black/docs/usage_and_configuration/file_collection_and_discovery.md

File collection and discovery

You can directly pass Black files, but you can also pass directories and Black will walk them, collecting files to format. It determines what files to format or skip automatically using the inclusion and exclusion regexes and as well their modification time.

Ignoring unmodified files

Black remembers files it has already formatted, unless the --diff flag is used or code is passed via standard input. This information is stored per-user. The exact location of the file depends on the Black version and the system on which Black is run. The file is non-portable. The standard location on common operating systems is:

• Windows: C:\Users\<username>\AppData\Local\black\black\Cache\<version>\cache.<line-length>.<file-mode>.pickle
• macOS: /Users/<username>/Library/Caches/black/<version>/cache.<line-length>.<file-mode>.pickle
• Linux: /home/<username>/.cache/black/<version>/cache.<line-length>.<file-mode>.pickle

file-mode is an int flag that determines whether the file was formatted as 3.6+ only, as .pyi, and whether string normalization was omitted.

To override the location of these files on all systems, set the environment variable BLACK_CACHE_DIR to the preferred location. Alternatively on macOS and Linux, set XDG_CACHE_HOME to your preferred location. For example, if you want to put the cache in the directory you're running Black from, set BLACK_CACHE_DIR=.cache/black. Black will then write the above files to .cache/black. Note that BLACK_CACHE_DIR will take precedence over XDG_CACHE_HOME if both are set.

Disabling the cache with --no-cache

If you need Black to always perform a fresh analysis and not consult or update the on-disk cache, use the --no-cache flag. When provided, Black will neither read from nor write to the per-user cache. This is useful for debugging, for CI runs where you want a deterministic fresh run, or when you suspect cache corruption.

Example:

python -m black --no-cache .

.gitignore

If --exclude is not set, Black will automatically ignore files and directories in .gitignore file(s), if present.

If you want Black to continue using .gitignore while also configuring the exclusion rules, please use --extend-exclude.