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# Pragmatism

Early versions of _Black_ used to be absolutist in some respects. They took after its
initial author. This was fine at the time as it made the implementation simpler and
there were not many users anyway. Not many edge cases were reported. As a mature tool,
_Black_ does make some exceptions to rules it otherwise holds. This section documents
what those exceptions are and why this is the case.

## 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:

```py3
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.

## r"strings" and R"strings"

_Black_ normalizes string quotes as well as string prefixes, making them lowercase. One
exception to this rule is r-strings. It turns out that the very popular
[MagicPython](https://github.com/MagicStack/MagicPython/) syntax highlighter, used by
default by (among others) GitHub and Visual Studio Code, differentiates between
r-strings and R-strings. The former are syntax highlighted as regular expressions while
the latter are treated as true raw strings with no special semantics.