_Black_ will add trailing commas to expressions that are split by comma where each
element is on its own line. This includes function signatures.
-Unnecessary trailing commas are removed if an expression fits in one line. This makes it
-1% more likely that your line won't exceed the allotted line length limit. Moreover, in
-this scenario, if you added another argument to your call, you'd probably fit it in the
-same line anyway. That doesn't make diffs any larger.
-
-One exception to removing trailing commas is tuple expressions with just one element. In
-this case _Black_ won't touch the single trailing comma as this would unexpectedly
-change the underlying data type. Note that this is also the case when commas are used
-while indexing. This is a tuple in disguise: `numpy_array[3, ]`.
-
One exception to adding trailing commas is function signatures containing `*`, `*args`,
or `**kwargs`. In this case a trailing comma is only safe to use on Python 3.6. _Black_
will detect if your file is already 3.6+ only and use trailing commas in this situation.
comma in this situation and _Black_ didn't recognize it was safe to do so, put it there
manually and _Black_ will keep it.
+A pre-existing trailing comma informs _Black_ to always explode contents of the current
+bracket pair into one item per line. Read more about this in the
+[Pragmatism](#pragmatism) section below.
+
### Strings
_Black_ prefers double quotes (`"` and `"""`) over single quotes (`'` and `'''`). It
How do you make it stop? Just delete that trailing comma and _Black_ will collapse your
collection into one line if it fits.
+If you must, you can recover the behaviour of early versions of Black with the option
+`--skip-magic-trailing-comma` / `-C`.
+
### r"strings" and R"strings"
_Black_ normalizes string quotes as well as string prefixes, making them lowercase. One
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