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
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, when we implement this, format it like this:
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
--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
contextlib.ExitStack to combine context managers in the
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()) ...
Experimental, potentially disruptive style changes are gathered under the
CLI flag. At the end of each year, these changes may be adopted into the default style,
as described in The Black Code Style. 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.