future_style.md

The (future of the) Black code style

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 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:

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 eventually format it like this:

with \
     make_context_manager(1) as cm1, \
     make_context_manager(2) as cm2, \
     make_context_manager(3) as cm3, \
     make_context_manager(4) as cm4 \
:
    ...  # backslashes and an ugly stranded colon

Although when the target version is Python 3.9 or higher, Black will use parentheses instead since they're allowed in Python 3.9 and higher.

Improved string processing

Currently, Black does not split long strings to fit the line length limit. Currently, there is an experimental option to enable splitting strings. We plan to enable this option by default once it is fully stable. This is tracked in this issue.

Preview style

Potentially disruptive style changes between major releases are gathered under the --preview CLI flag. They will eventually become part of main functionality, but until then are described here.