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Fix false alarm in E203 rule (issue #373, black incompatibility) #914

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Fix false alarm in E203 rule (issue #373, black incompatibility) #914

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86a51c5
Fix false alarm in E203 rule.
DesbyP Feb 28, 2020
7400aff
Add support for nested lambda expression in brackets
DesbyP Feb 28, 2020
c88d21e
ironically remove space to comply with flake8
DesbyP Feb 28, 2020
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44 changes: 43 additions & 1 deletion pycodestyle.py
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Original file line number Diff line number Diff line change
Expand Up @@ -413,6 +413,12 @@ def extraneous_whitespace(logical_line):
- Immediately inside parentheses, brackets or braces.
- Immediately before a comma, semicolon, or colon.

Exceptions:
- When the colon acts as a slice, the rule of binary operators
applies and we should have the same amount of space on either side
- When the colon acts as a slice but a parameter is omitted, then
the space is omitted

Okay: spam(ham[1], {eggs: 2})
E201: spam( ham[1], {eggs: 2})
E201: spam(ham[ 1], {eggs: 2})
Expand All @@ -421,10 +427,45 @@ def extraneous_whitespace(logical_line):
E202: spam(ham[1 ], {eggs: 2})
E202: spam(ham[1], {eggs: 2 })

Okay: ham[8 : 2]
Okay: ham[: 2]
E203: if x == 4: print x, y; x, y = y , x
E203: if x == 4: print x, y ; x, y = y, x
E203: if x == 4 : print x, y; x, y = y, x
"""

def is_a_slice(line, space_pos):
"""Check if the colon after an extra space acts as a slice

Return True if the colon is directly contained within
square brackets.
"""
# list of found '[({' as tuples "(char, position)"
parentheses_brackets_braces = list()
for i in range(space_pos):
c = line[i]
if c in '[({':
# add it to the stack
parentheses_brackets_braces.append((c, i))
elif c in '])}':
# unstack last item and check consistency
last_opened = parentheses_brackets_braces.pop()[0]
expected_close = {'{': '}', '(': ')', '[': ']'}[last_opened]
if c != expected_close: # invalid Python code
return False
is_within_brackets = (len(parentheses_brackets_braces) > 0 and
parentheses_brackets_braces[-1][0] == '[')

is_lambda_expr = False
if is_within_brackets:
# check for a lambda expression nested in brackets
if space_pos > 6:
last_opened = parentheses_brackets_braces[-1]
between_bracket_colon = line[last_opened[1] + 1: space_pos]
is_lambda_expr = 'lambda' in between_bracket_colon

return (is_within_brackets and not is_lambda_expr)

line = logical_line
for match in EXTRANEOUS_WHITESPACE_REGEX.finditer(line):
text = match.group()
Expand All @@ -433,7 +474,8 @@ def extraneous_whitespace(logical_line):
if text == char + ' ':
# assert char in '([{'
yield found + 1, "E201 whitespace after '%s'" % char
elif line[found - 1] != ',':
elif (line[found - 1] != ',' and
not (char == ':' and is_a_slice(line, found))):
Comment on lines +477 to +478
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Suggested change
elif (line[found - 1] != ',' and
not (char == ':' and is_a_slice(line, found))):
elif (line[found - 1] != ','
and not (char == ':' and is_a_slice(line, found))):

I was under the impression that 'pythonic' style puts the binary operator after a line break, not before.

--- Personal preference / opinion only below this line. Disregard at your pleasure ---

I personally also prefer to format multi-line conditions like this:

        elif (
            line[found - 1] != ','
            and not (char == ':' and is_a_slice(line, found))
        ):

because it puts co-ordinate conditions in a visually co-ordinate structure, and also has dedicated lines to mark the bounds of the compound condition. (i.e. the elif ( and ): lines, visually positioned to encapsulate the conditions and indicate that they're subordinate to the elif construct itself. It does take up a lot more vertical space though, so I can understand why some might dislike that.

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Guess this is the right pep for this:
https://www.python.org/dev/peps/pep-0008/#should-a-line-break-before-or-after-a-binary-operator

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@hoylemd I agree and prefer this coding style as well.
Yet W503 in TravisCI prevents me of doing so :

pycodestyle.py:489:13: W503 line break before binary operator
pycodestyle.py:512:13: W503 line break before binary operator

If @s-weigand suggestion to ignore W503 was accepted then we could proceed :)

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@FichteFoll FichteFoll Aug 14, 2020 •
edited
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I was under the impression that 'pythonic' style puts the binary operator after a line break, not before.

This was changed only a few years back (roughly when W504 was introduced and both were added to the default ignore list). pycodestyle itself does not use this style of line breaks before binary operators and you should always adhere to the project's style.

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thank you for the precision
Then I guess the PR is ok for review

code = ('E202' if char in '}])' else 'E203') # if char in ',;:'
yield found, "%s whitespace before '%s'" % (code, char)

Expand Down
12 changes: 12 additions & 0 deletions testsuite/E20.py
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Original file line number Diff line number Diff line change
Expand Up @@ -46,10 +46,22 @@
if x == 4:
print x, y
x, y = y , x
#: E203:1:37
foo[idxs[2 : 6] : spam(ham[1], {eggs : a[2 : 4]})]
#: E203:1:8
[lambda : foo]
#: E203:1:13
ham[lambda x : foo]
#: Okay
if x == 4:
print x, y
x, y = y, x
a[b1, :] == a[b1, ...]
b = a[:, b1]
ham[1:9], ham[1:9:3], ham[:9:3], ham[1::3], ham[1:9:]
ham[: upper_fn(x) : step_fn(x)], ham[:: step_fn(x)]
ham[lower + offset : upper + offset]
foo[idxs[2 : 6] : spam(ham[1], {eggs: a[2 : 4]})]
[lambda: foo]
ham[lambda x: foo]
#: