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Black Python formatter

Black reformats entire files in place. It doesn’t reformat lines that end with # fmt: skip or blocks that start with # fmt: off and end with # fmt: on. # fmt: on/off must be on the same level of indentation and in the same block, meaning no unindents beyond the initial indentation level between them. It also recognizes YAPF’s block comments to the same effect, as a courtesy for straddling code.

The magic trailing comma
Black in general does not take existing formatting into account.

However, there are cases where you put a short collection or function call in your code but you anticipate it will grow in the future.

For example:

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TRANSLATIONS = {
    "en_us": "English (US)",
    "pl_pl": "polski",
}

Early versions of Black used to ruthlessly collapse those into one line (it fits!). Now, you can communicate that you don’t want that by putting a trailing comma in the collection yourself. When you do, Black will know to always explode your collection into one item per line.

How do you make it stop? Just delete that trailing comma and Black will collapse your collection into one line if it fits.

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