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Only use trailing commas in function signatures when it's safe

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Trailing commas after * or ** in a function signature are only safe for Python 3.6
code.  So now Black checks whether the file was already Python 3.6 to begin
with.  If so, trailing commas are used in such cases.  Otherwise, they're not.

When * and ** don't appear in a function signature, the trailing comma is
always safe.

Fixes #8
This commit is contained in:
Łukasz Langa 2018-03-15 19:25:23 -07:00 committed by Lukasz Langa
parent c26daa4fd5
commit 5fb5cc8c2b
6 changed files with 101 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
README.md
View File

@ -260,6 +260,11 @@ You can still try but prepare to be disappointed.
* added `--check`
* only put trailing commas in function signatures and calls if it's
safe to do so. If the file is Python 3.6+ it's always safe, otherwise
only safe if there are no `*args` or `**kwargs` used in the signature
or call. (#8)
* fixed invalid spacing of dots in relative imports (#6, #13)
* fixed invalid splitting after comma on unpacked variables in for-loops

62
black.py
View File

@ -7,6 +7,7 @@
import os
from pathlib import Path
import tokenize
import sys
from typing import (
Dict, Generic, Iterable, Iterator, List, Optional, Set, Tuple, TypeVar, Union
)
@ -192,6 +193,7 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
comments: List[Line] = []
lines = LineGenerator()
elt = EmptyLineTracker()
py36 = is_python36(src_node)
empty_line = Line()
after = 0
for current_line in lines.visit(src_node):
@ -204,7 +206,7 @@ def format_str(src_contents: str, line_length: int) -> FileContent:
for comment in comments:
dst_contents += str(comment)
comments = []
for line in split_line(current_line, line_length=line_length):
for line in split_line(current_line, line_length=line_length, py36=py36):
dst_contents += str(line)
else:
comments.append(current_line)
@ -1108,13 +1110,18 @@ def generate_comments(leaf: Leaf) -> Iterator[Leaf]:
yield Leaf(STANDALONE_COMMENT, line)
def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Line]:
def split_line(
line: Line, line_length: int, inner: bool = False, py36: bool = False
) -> Iterator[Line]:
"""Splits a `line` into potentially many lines.
They should fit in the allotted `line_length` but might not be able to.
`inner` signifies that there were a pair of brackets somewhere around the
current `line`, possibly transitively. This means we can fallback to splitting
by delimiters if the LHS/RHS don't yield any results.
If `py36` is True, splitting may generate syntax that is only compatible
with Python 3.6 and later.
"""
line_str = str(line).strip('\n')
if len(line_str) <= line_length and '\n' not in line_str:
@ -1137,11 +1144,13 @@ def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Li
# split altogether.
result: List[Line] = []
try:
for l in split_func(line):
for l in split_func(line, py36=py36):
if str(l).strip('\n') == line_str:
raise CannotSplit("Split function returned an unchanged result")
result.extend(split_line(l, line_length=line_length, inner=True))
result.extend(
split_line(l, line_length=line_length, inner=True, py36=py36)
)
except CannotSplit as cs:
continue
@ -1153,7 +1162,7 @@ def split_line(line: Line, line_length: int, inner: bool = False) -> Iterator[Li
yield line
def left_hand_split(line: Line) -> Iterator[Line]:
def left_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
"""Split line into many lines, starting with the first matching bracket pair.
Note: this usually looks weird, only use this for function definitions.
@ -1208,7 +1217,7 @@ def left_hand_split(line: Line) -> Iterator[Line]:
yield result
def right_hand_split(line: Line) -> Iterator[Line]:
def right_hand_split(line: Line, py36: bool = False) -> Iterator[Line]:
"""Split line into many lines, starting with the last matching bracket pair."""
head = Line(depth=line.depth)
body = Line(depth=line.depth + 1, inside_brackets=True)
@ -1259,10 +1268,12 @@ def right_hand_split(line: Line) -> Iterator[Line]:
yield result
def delimiter_split(line: Line) -> Iterator[Line]:
def delimiter_split(line: Line, py36: bool = False) -> Iterator[Line]:
"""Split according to delimiters of the highest priority.
This kind of split doesn't increase indentation.
If `py36` is True, the split will add trailing commas also in function
signatures that contain * and **.
"""
try:
last_leaf = line.leaves[-1]
@ -1276,11 +1287,20 @@ def delimiter_split(line: Line) -> Iterator[Line]:
raise CannotSplit("No delimiters found")
current_line = Line(depth=line.depth, inside_brackets=line.inside_brackets)
lowest_depth = sys.maxsize
trailing_comma_safe = True
for leaf in line.leaves:
current_line.append(leaf, preformatted=True)
comment_after = line.comments.get(id(leaf))
if comment_after:
current_line.append(comment_after, preformatted=True)
lowest_depth = min(lowest_depth, leaf.bracket_depth)
if (
leaf.bracket_depth == lowest_depth and # type: ignore
leaf.type == token.STAR or
leaf.type == token.DOUBLESTAR
):
trailing_comma_safe = trailing_comma_safe and py36
leaf_priority = delimiters.get(id(leaf))
if leaf_priority == delimiter_priority:
normalize_prefix(current_line.leaves[0])
@ -1290,7 +1310,8 @@ def delimiter_split(line: Line) -> Iterator[Line]:
if current_line:
if (
delimiter_priority == COMMA_PRIORITY and
current_line.leaves[-1].type != token.COMMA
current_line.leaves[-1].type != token.COMMA and
trailing_comma_safe
):
current_line.append(Leaf(token.COMMA, ','))
normalize_prefix(current_line.leaves[0])
@ -1325,6 +1346,31 @@ def normalize_prefix(leaf: Leaf) -> None:
leaf.prefix = ''
def is_python36(node: Node) -> bool:
"""Returns True if the current file is using Python 3.6+ features.
Currently looking for:
- f-strings; and
- trailing commas after * or ** in function signatures.
"""
for n in node.pre_order():
if n.type == token.STRING:
assert isinstance(n, Leaf)
if n.value[:2] in {'f"', 'F"', "f'", "F'", 'rf', 'fr', 'RF', 'FR'}:
return True
elif (
n.type == syms.typedargslist and
n.children and
n.children[-1].type == token.COMMA
):
for ch in n.children:
if ch.type == token.STAR or ch.type == token.DOUBLESTAR:
return True
return False
PYTHON_EXTENSIONS = {'.py'}
BLACKLISTED_DIRECTORIES = {
'build', 'buck-out', 'dist', '_build', '.git', '.hg', '.mypy_cache', '.tox', '.venv'

18
tests/expression.py
View File

@ -71,6 +71,7 @@
call(kwarg='hey')
call(arg, kwarg='hey')
call(arg, another, kwarg='hey', **kwargs)
call(this_is_a_very_long_variable_which_will_force_a_delimiter_split, arg, another, kwarg='hey', **kwargs) # note: no trailing comma pre-3.6
lukasz.langa.pl
call.me(maybe)
1 .real
@ -88,11 +89,6 @@
slice[1:]
slice[::-1]
(str or None) if (sys.version_info[0] > (3,)) else (str or bytes or None)
f'f-string without formatted values is just a string'
f'{{NOT a formatted value}}'
f'some f-string with {a} {few():.2f} {formatted.values!r}'
f"{f'{nested} inner'} outer"
f'space between opening braces: { {a for a in (1, 2, 3)}}'
{'2.7': dead, '3.7': long_live or die_hard}
{'2.7', '3.6', '3.7', '3.8', '3.9', '4.0' if gilectomy else '3.10'}
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or A, 11 or B, 12 or C]
@ -200,6 +196,13 @@ async def f():
call(kwarg='hey')
call(arg, kwarg='hey')
call(arg, another, kwarg='hey', **kwargs)
call(
this_is_a_very_long_variable_which_will_force_a_delimiter_split,
arg,
another,
kwarg='hey',
**kwargs
) # note: no trailing comma pre-3.6
lukasz.langa.pl
call.me(maybe)
1 .real
@ -217,11 +220,6 @@ async def f():
slice[1:]
slice[::-1]
(str or None) if (sys.version_info[0] > (3,)) else (str or bytes or None)
f'f-string without formatted values is just a string'
f'{{NOT a formatted value}}'
f'some f-string with {a} {few():.2f} {formatted.values!r}'
f"{f'{nested} inner'} outer"
f'space between opening braces: { {a for a in (1, 2, 3)}}'
{'2.7': dead, '3.7': long_live or die_hard}
{'2.7', '3.6', '3.7', '3.8', '3.9', '4.0' if gilectomy else '3.10'}
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or A, 11 or B, 12 or C]

5
tests/fstring.py Normal file
View File

@ -0,0 +1,5 @@
f'f-string without formatted values is just a string'
f'{{NOT a formatted value}}'
f'some f-string with {a} {few():.2f} {formatted.values!r}'
f"{f'{nested} inner'} outer"
f'space between opening braces: { {a for a in (1, 2, 3)}}'

4
tests/function.py
View File

@ -6,7 +6,7 @@
from library import some_connection, \
some_decorator
f'trigger 3.6 mode'
def func_no_args():
a; b; c
if True: raise RuntimeError
@ -71,6 +71,8 @@ def long_lines():
from library import some_connection, some_decorator
f'trigger 3.6 mode'
def func_no_args():
a

26
tests/test_black.py
View File

@ -108,6 +108,14 @@ def test_expression(self) -> None:
black.assert_equivalent(source, actual)
black.assert_stable(source, actual, line_length=ll)
@patch("black.dump_to_file", dump_to_stderr)
def test_fstring(self) -> None:
source, expected = read_data('fstring')
actual = fs(source)
self.assertFormatEqual(expected, actual)
black.assert_equivalent(source, actual)
black.assert_stable(source, actual, line_length=ll)
@patch("black.dump_to_file", dump_to_stderr)
def test_comments(self) -> None:
source, expected = read_data('comments')
@ -215,6 +223,24 @@ def err(msg: str, **kwargs):
)
self.assertEqual(report.return_code, 123)
def test_is_python36(self):
node = black.lib2to3_parse("def f(*, arg): ...\n")
self.assertFalse(black.is_python36(node))
node = black.lib2to3_parse("def f(*, arg,): ...\n")
self.assertTrue(black.is_python36(node))
node = black.lib2to3_parse("def f(*, arg): f'string'\n")
self.assertTrue(black.is_python36(node))
source, expected = read_data('function')
node = black.lib2to3_parse(source)
self.assertTrue(black.is_python36(node))
node = black.lib2to3_parse(expected)
self.assertTrue(black.is_python36(node))
source, expected = read_data('expression')
node = black.lib2to3_parse(source)
self.assertFalse(black.is_python36(node))
node = black.lib2to3_parse(expected)
self.assertFalse(black.is_python36(node))
if __name__ == '__main__':
unittest.main()