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Bump peter-evans/create-or-update-comment from 2.0.0 to 2.0.1 (#3354)
[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_manager1() as cm1, \
27      make_context_manager2() as cm2, \
28      make_context_manager3() as cm3, \
29      make_context_manager4() 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 An alternative to consider if the backslashes in the above formatting are undesirable is
38 to use {external:py:obj}`contextlib.ExitStack` to combine context managers in the
39 following way:
40
41 ```python
42 with contextlib.ExitStack() as exit_stack:
43     cm1 = exit_stack.enter_context(make_context_manager1())
44     cm2 = exit_stack.enter_context(make_context_manager2())
45     cm3 = exit_stack.enter_context(make_context_manager3())
46     cm4 = exit_stack.enter_context(make_context_manager4())
47     ...
48 ```
49
50 ## Preview style
51
52 Experimental, potentially disruptive style changes are gathered under the `--preview`
53 CLI flag. At the end of each year, these changes may be adopted into the default style,
54 as described in [The Black Code Style](./index.rst). Because the functionality is
55 experimental, feedback and issue reports are highly encouraged!
56
57 ### Improved string processing
58
59 _Black_ will split long string literals and merge short ones. Parentheses are used where
60 appropriate. When split, parts of f-strings that don't need formatting are converted to
61 plain strings. User-made splits are respected when they do not exceed the line length
62 limit. Line continuation backslashes are converted into parenthesized strings.
63 Unnecessary parentheses are stripped. The stability and status of this feature is
64 tracked in [this issue](https://github.com/psf/black/issues/2188).
65
66 ### Removing newlines in the beginning of code blocks
67
68 _Black_ will remove newlines in the beginning of new code blocks, i.e. when the
69 indentation level is increased. For example:
70
71 ```python
72 def my_func():
73
74     print("The line above me will be deleted!")
75 ```
76
77 will be changed to:
78
79 ```python
80 def my_func():
81     print("The line above me will be deleted!")
82 ```
83
84 This new feature will be applied to **all code blocks**: `def`, `class`, `if`, `for`,
85 `while`, `with`, `case` and `match`.
86
87 ### Improved parentheses management
88
89 _Black_ will format parentheses around return annotations similarly to other sets of
90 parentheses. For example:
91
92 ```python
93 def foo() -> (int):
94     ...
95
96 def foo() -> looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong:
97     ...
98 ```
99
100 will be changed to:
101
102 ```python
103 def foo() -> int:
104     ...
105
106
107 def foo() -> (
108     looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong
109 ):
110     ...
111 ```
112
113 And, extra parentheses in `await` expressions and `with` statements are removed. For
114 example:
115
116 ```python
117 with ((open("bla.txt")) as f, open("x")):
118     ...
119
120 async def main():
121     await (asyncio.sleep(1))
122 ```
123
124 will be changed to:
125
126 ```python
127 with open("bla.txt") as f, open("x"):
128     ...
129
130
131 async def main():
132     await asyncio.sleep(1)
133 ```