## Code style
-_Black_ reformats entire files in place. Style configuration options are deliberately
-limited and rarely added. It doesn't take previous formatting into account, except for
-the magic trailing comma and preserving newlines. It doesn't reformat blocks that start
-with `# fmt: off` and end with `# fmt: on`, or lines that ends with `# fmt: skip`.
+_Black_ aims for consistency, generality, readability and reducing git diffs. Similar
+language constructs are formatted with similar rules. Style configuration options are
+deliberately limited and rarely added. Previous formatting is taken into account as
+little as possible, with rare exceptions like the magic trailing comma. The coding style
+used by _Black_ can be viewed as a strict subset of PEP 8.
+
+_Black_ reformats entire files in place. It doesn't reformat blocks that start with
+`# fmt: off` and end with `# fmt: on`, or lines that ends with `# fmt: skip`.
`# fmt: on/off` have to be on the same level of indentation. It also recognizes
[YAPF](https://github.com/google/yapf)'s block comments to the same effect, as a
courtesy for straddling code.
+The rest of this document describes the current formatting style. If you're interested
+in trying out where the style is heading, see [future style](./future_style.md) and try
+running `black --preview`.
+
### How _Black_ wraps lines
_Black_ ignores previous formatting and applies uniform horizontal and vertical
whitespace to your code. The rules for horizontal whitespace can be summarized as: do
-whatever makes `pycodestyle` happy. The coding style used by _Black_ can be viewed as a
-strict subset of PEP 8.
+whatever makes `pycodestyle` happy.
As for vertical whitespace, _Black_ tries to render one full expression or simple
statement per line. If this fits the allotted line length, great.
If a data structure literal (tuple, list, set, dict) or a line of "from" imports cannot
fit in the allotted length, it's always split into one element per line. This minimizes
diffs as well as enables readers of code to find which commit introduced a particular
-entry. This also makes _Black_ compatible with [isort](https://pypi.org/p/isort/) with
-the following configuration.
-
-<details>
-<summary>A compatible `.isort.cfg`</summary>
-
-```cfg
-[settings]
-multi_line_output = 3
-include_trailing_comma = True
-force_grid_wrap = 0
-use_parentheses = True
-ensure_newline_before_comments = True
-line_length = 88
-```
-
-The equivalent command line is:
-
-```
-$ isort --multi-line=3 --trailing-comma --force-grid-wrap=0 --use-parentheses --line-width=88 [ file.py ]
-```
-
-</details>
+entry. This also makes _Black_ compatible with
+[isort](../guides/using_black_with_other_tools.md#isort) with the ready-made `black`
+profile or manual configuration.
### Line length
_Black_ won't insert empty lines after function docstrings unless that empty line is
required due to an inner function starting immediately after.
+### Comments
+
+_Black_ does not format comment contents, but it enforces two spaces between code and a
+comment on the same line, and a space before the comment text begins. Some types of
+comments that require specific spacing rules are respected: doc comments (`#: comment`),
+section comments with long runs of hashes, and Spyder cells. Non-breaking spaces after
+hashes are also preserved. Comments may sometimes be moved because of formatting
+changes, which can break tools that assign special meaning to them. See
+[AST before and after formatting](#ast-before-and-after-formatting) for more discussion.
+
### Trailing commas
_Black_ will add trailing commas to expressions that are split by comma where each
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.
+_Black_ also standardizes string prefixes. Prefix characters are made lowercase with the
+exception of [capital "R" prefixes](#rstrings-and-rstrings), unicode literal markers
+(`u`) are removed because they are meaningless in Python 3, and in the case of multiple
+characters "r" is put first as in spoken language: "raw f-string".
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
you can pass `--skip-string-normalization` on the command line. This is meant as an
adoption helper, avoid using this for new projects.
-As an experimental option (can be enabled by `--experimental-string-processing`),
-_Black_ splits long strings (using parentheses where appropriate) and merges short ones.
-When split, parts of f-strings that don't need formatting are converted to plain
-strings. User-made splits are respected when they do not exceed the line length limit.
-Line continuation backslashes are converted into parenthesized strings. Unnecessary
-parentheses are stripped. Because the functionality is experimental, feedback and issue
-reports are highly encouraged!
-
_Black_ also processes docstrings. Firstly the indentation of docstrings is corrected
for both quotations and the text within, although relative indentation in the text is
preserved. Superfluous trailing whitespace on each line and unnecessary new lines at the
end of the docstring are removed. All leading tabs are converted to spaces, but tabs
inside text are preserved. Whitespace leading and trailing one-line docstrings is
-removed. The quotations of an empty docstring are separated with one space.
+removed.
### Numeric literals
_Black_ standardizes most numeric literals to use lowercase letters for the syntactic
parts and uppercase letters for the digits themselves: `0xAB` instead of `0XAB` and
-`1e10` instead of `1E10`. Python 2 long literals are styled as `2L` instead of `2l` to
-avoid confusion between `l` and `1`.
+`1e10` instead of `1E10`.
### Line breaks & binary operators
[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.
+Almost all operators will be surrounded by single spaces, the only exceptions are unary
+operators (`+`, `-`, and `~`), and power operators when both operands are simple. For
+powers, an operand is considered simple if it's only a NAME, numeric CONSTANT, or
+attribute access (chained attribute access is allowed), with or without a preceding
+unary operator.
+
+```python
+# For example, these won't be surrounded by whitespace
+a = x**y
+b = config.base**5.2
+c = config.base**runtime.config.exponent
+d = 2**5
+e = 2**~5
+
+# ... but these will be surrounded by whitespace
+f = 2 ** get_exponent()
+g = get_x() ** get_y()
+h = config['base'] ** 2
+```
+
### Slices
PEP 8
projects / etc / vim.git / blobdiff