psf/black

List concatenation, multiple lines

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#260 opened on May 26, 2018

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 (2 comments) (3 reactions) (0 assignees)Python (41,258 stars) (2,693 forks)batch import
F: linebreakF: symmetryT: enhancementT: stylehelp wanted

Description

Probably not a bug, but I was wondering if the code below shouldn't be formatted more like call chains are. I did not expect black to change anything other than quotes in this example. Aligned brackets feel much more readable.

# before
-    search_fields = (
-        ['file__%s' % field for field in FileAdmin.search_fields] +
-        ['resource__%s' % field for field in ResourceAdmin.search_fields]
-    )
# black output
+    search_fields = ["file__%s" % field for field in FileAdmin.search_fields] + [
+        "resource__%s" % field for field in ResourceAdmin.search_fields
+    ]

Operating system: OSX 10.11.6 Python version: 3.6.5 Black version: 18.5b0 Does also happen on master: yes

Contributor guide

Tech stack
python
Domain
tooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Python 3.6+Familiarity with Black's codebase
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
This issue requests that list concatenation on multiple lines be formatted similarly to call chains. Investigate how Black currently handles binary expressions involving list comprehensions, particularly in the blib2to3 or lines module. Consider adjusting the split logic so that the + operator is placed at the beginning of the continuation line, aligning with the style used for chained calls. Test the provided example to ensure the output matches the proposed formatting.