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docs: We're not going to use backslashes for the with statement (#4564)

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Jelle Zijlstra 2025-01-28 18:29:05 -08:00 committed by GitHub
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docs/the_black_code_style/future_style.md
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@ -2,6 +2,8 @@
## Preview style ## Preview style
(labels/preview-style)=
Experimental, potentially disruptive style changes are gathered under the `--preview` Experimental, potentially disruptive style changes are gathered under the `--preview`
CLI flag. At the end of each year, these changes may be adopted into the default style, CLI flag. At the end of each year, these changes may be adopted into the default style,
as described in [The Black Code Style](index.md). Because the functionality is as described in [The Black Code Style](index.md). Because the functionality is
@ -262,52 +264,3 @@ s = ( # Top comment
# Bottom comment # Bottom comment
) )
``` ```
## Potential future changes
This section lists changes that we may want to make in the future, but that aren't
implemented yet.
### Using backslashes for with statements
[Backslashes are bad and should be never be used](labels/why-no-backslashes) however
there is one exception: `with` statements using multiple context managers. Before Python
3.9 Python's grammar does not allow organizing parentheses around the series of context
managers.
We don't want formatting like:
```py3
with make_context_manager1() as cm1, make_context_manager2() as cm2, make_context_manager3() as cm3, make_context_manager4() as cm4:
... # nothing to split on - line too long
```
So _Black_ will, when we implement this, format it like this:
```py3
with \
make_context_manager1() as cm1, \
make_context_manager2() as cm2, \
make_context_manager3() as cm3, \
make_context_manager4() as cm4 \
:
... # backslashes and an ugly stranded colon
```
Although when the target version is Python 3.9 or higher, _Black_ uses parentheses
instead in `--preview` mode (see below) since they're allowed in Python 3.9 and higher.
An alternative to consider if the backslashes in the above formatting are undesirable is
to use {external:py:obj}`contextlib.ExitStack` to combine context managers in the
following way:
```python
with contextlib.ExitStack() as exit_stack:
cm1 = exit_stack.enter_context(make_context_manager1())
cm2 = exit_stack.enter_context(make_context_manager2())
cm3 = exit_stack.enter_context(make_context_manager3())
cm4 = exit_stack.enter_context(make_context_manager4())
...
```
(labels/preview-style)=