# The (future of the) Black code style
`{warning}
Changes to this document often aren't tied and don't relate to releases of
_Black_. It's recommended that you read the latest version available.
`
## 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:
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)=
## Preview style
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, as described in [The Black Code Style](index.md). Because the functionality is experimental, feedback and issue reports are highly encouraged!
### Improved string processing
_Black_ will split long string literals and merge short ones. Parentheses are used where appropriate. 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. The stability and status of this feature is tracked in [this issue](https://github.com/psf/black/issues/2188).
### Improved line breaks
For assignment expressions, _Black_ now prefers to split and wrap the right side of the assignment instead of left side. For example:
“with_a_long_key”
- ] = some_looooooooong_module.some_looooooooooooooong_function_name(
first_argument, second_argument, third_argument
)¶
will be changed to:
```python some_dict[“with_a_long_key”] = (
- some_looooooooong_module.some_looooooooooooooong_function_name(
first_argument, second_argument, third_argument
)
)¶
### Improved parentheses management
For dict literals with long values, they are now wrapped in parentheses. Unnecessary parentheses are now removed. For example:
“a key in my dict”: a_very_long_variable * and_a_very_long_function_call() / 100000.0, “another key”: (short_value),
}¶
will be changed to:
- “a key in my dict”: (
a_very_long_variable * and_a_very_long_function_call() / 100000.0
), “another key”: short_value,
}¶
### Improved multiline string handling
_Black_ is smarter when formatting multiline strings, especially in function arguments, to avoid introducing extra line breaks. Previously, it would always consider multiline strings as not fitting on a single line. With this new feature, _Black_ looks at the context around the multiline string to decide if it should be inlined or split to a separate line. For example, when a multiline string is passed to a function, _Black_ will only split the multiline string if a line is too long or if multiple arguments are being passed.
For example, _Black_ will reformat
“””This is a multiline string
to:
This is a multiline string
And:
```python MULTILINE = “”” foobar “””.replace(
“n”, “”
)¶
to:
`python
MULTILINE = """
foobar
""".replace("\n", "")
`
Implicit multiline strings are special, because they can have inline comments. Strings without comments are merged, for example
“An ” “implicit ” “multiline ” “string”
)¶
becomes
`python
s = "An implicit multiline string"
`
A comment on any line of the string (or between two string lines) will block the merging, so
“An “ # Important comment concerning just this line “implicit ” “multiline ” “string”
)¶
and
“An ” “implicit ” # Comment in between “multiline ” “string”
)¶
will not be merged. Having the comment after or before the string lines (but still inside the parens) will merge the string. For example
“An ” “implicit ” “multiline ” “string” # Bottom comment
)¶
becomes
“An implicit multiline string” # Bottom comment