+after module-level functions and classes. *Black* will not put empty
+lines between function/class definitions and standalone comments that
+immediately precede the given function/class.
+
+*Black* will enforce single empty lines between a class-level docstring
+and the first following field or method. This conforms to
+[PEP 257](https://www.python.org/dev/peps/pep-0257/#multi-line-docstrings).
+
+*Black* won't insert empty lines after function docstrings unless that
+empty line is required due to an inner function starting immediately
+after.
+
+
+### Trailing commas
+
+*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. If you
+wonder how it knows, it looks for f-strings and existing use of trailing
+commas in function signatures that have stars in them. In other words,
+if you'd like a trailing comma in this situation and *Black* didn't
+recognize it was safe to do so, put it there manually and *Black* will
+keep it.
+
+
+### Strings
+
+*Black* prefers double quotes (`"` and `"""`) over single quotes (`'`
+and `'''`). It will replace the latter with the former as long as it
+does not result in more backslash escapes than before.
+
+*Black* also standardizes string prefixes, making them always lowercase.
+On top of that, if your code is already Python 3.6+ only or it's using
+the `unicode_literals` future import, *Black* will remove `u` from the
+string prefix as it is meaningless in those scenarios.
+
+The main reason to standardize on a single form of quotes is aesthetics.
+Having one kind of quotes everywhere reduces reader distraction.
+It will also enable a future version of *Black* to merge consecutive
+string literals that ended up on the same line (see
+[#26](https://github.com/ambv/black/issues/26) for details).
+
+Why settle on double quotes? They anticipate apostrophes in English
+text. They match the docstring standard described in PEP 257. An
+empty string in double quotes (`""`) is impossible to confuse with
+a one double-quote regardless of fonts and syntax highlighting used.
+On top of this, double quotes for strings are consistent with C which
+Python interacts a lot with.
+
+On certain keyboard layouts like US English, typing single quotes is
+a bit easier than double quotes. The latter requires use of the Shift
+key. My recommendation here is to keep using whatever is faster to type
+and let *Black* handle the transformation.
+
+
+### Line breaks & binary operators
+
+*Black* will break a line before a binary operator when splitting a block
+of code over multiple lines. This is so that *Black* is compliant with the
+recent changes in the [PEP 8](https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator)
+style guide, which emphasizes that this approach improves readability.
+
+This behaviour may raise ``W503 line break before binary operator`` warnings in
+style guide enforcement tools like Flake8. Since ``W503`` is not PEP 8 compliant,
+you should tell Flake8 to ignore these warnings.
+
+
+### Slices
+
+PEP 8 [recommends](https://www.python.org/dev/peps/pep-0008/#whitespace-in-expressions-and-statements)
+to treat ``:`` in slices as a binary operator with the lowest priority, and to
+leave an equal amount of space on either side, except if a parameter is omitted
+(e.g. ``ham[1 + 1 :]``). It also states that for extended slices, both ``:``
+operators have to have the same amount of spacing, except if a parameter is
+omitted (``ham[1 + 1 ::]``). *Black* enforces these rules consistently.
+
+This behaviour may raise ``E203 whitespace before ':'`` warnings in style guide
+enforcement tools like Flake8. Since ``E203`` is not PEP 8 compliant, you should
+tell Flake8 to ignore these warnings.
+
+
+### Parentheses
+
+Some parentheses are optional in the Python grammar. Any expression can
+be wrapped in a pair of parentheses to form an atom. There are a few
+interesting cases:
+
+- `if (...):`
+- `while (...):`
+- `for (...) in (...):`
+- `assert (...), (...)`
+- `from X import (...)`
+- assignments like:
+ - `target = (...)`
+ - `target: type = (...)`
+ - `some, *un, packing = (...)`
+ - `augmented += (...)`
+
+In those cases, parentheses are removed when the entire statement fits
+in one line, or if the inner expression doesn't have any delimiters to
+further split on. If there is only a single delimiter and the expression
+starts or ends with a bracket, the parenthesis can also be successfully
+omitted since the existing bracket pair will organize the expression
+neatly anyway. Otherwise, the parentheses are added.
+
+Please note that *Black* does not add or remove any additional nested
+parentheses that you might want to have for clarity or further
+code organization. For example those parentheses are not going to be
+removed:
+```py3
+return not (this or that)
+decision = (maybe.this() and values > 0) or (maybe.that() and values < 0)
+```
+
+
+### Call chains
projects / etc / vim.git / blobdiff