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[etc/vim.git] / docs / the_black_code_style / future_style.md
1 # The (future of the) Black code style
2
3 ```{warning}
4 Changes to this document often aren't tied and don't relate to releases of
5 _Black_. It's recommended that you read the latest version available.
6 ```
7
8 ## Using backslashes for with statements
9
10 [Backslashes are bad and should be never be used](labels/why-no-backslashes) however
11 there is one exception: `with` statements using multiple context managers. Before Python
12 3.9 Python's grammar does not allow organizing parentheses around the series of context
13 managers.
14
15 We don't want formatting like:
16
17 ```py3
18 with make_context_manager1() as cm1, make_context_manager2() as cm2, make_context_manager3() as cm3, make_context_manager4() as cm4:
19     ...  # nothing to split on - line too long
20 ```
21
22 So _Black_ will eventually format it like this:
23
24 ```py3
25 with \
26      make_context_manager(1) as cm1, \
27      make_context_manager(2) as cm2, \
28      make_context_manager(3) as cm3, \
29      make_context_manager(4) as cm4 \
30 :
31     ...  # backslashes and an ugly stranded colon
32 ```
33
34 Although when the target version is Python 3.9 or higher, _Black_ will use parentheses
35 instead since they're allowed in Python 3.9 and higher.
36
37 ## Preview style
38
39 Experimental, potentially disruptive style changes are gathered under the `--preview`
40 CLI flag. At the end of each year, these changes may be adopted into the default style,
41 as described in [The Black Code Style](./index.rst). Because the functionality is
42 experimental, feedback and issue reports are highly encouraged!
43
44 ### Improved string processing
45
46 _Black_ will split long string literals and merge short ones. Parentheses are used where
47 appropriate. When split, parts of f-strings that don't need formatting are converted to
48 plain strings. User-made splits are respected when they do not exceed the line length
49 limit. Line continuation backslashes are converted into parenthesized strings.
50 Unnecessary parentheses are stripped. The stability and status of this feature is
51 tracked in [this issue](https://github.com/psf/black/issues/2188).