This adds separate C82X codes for cases when a trailing comma is required in an enclosure with a single element. The reason is that sometimes people prefer not to have to add comas when for the enclosure is used mostly for grouping. For example:

logger.info(
    'This is a long and excessively detailed '
    'possibly multi-line '
    'log message.'  # C822 missing trailing comma in one element enclosure
)

C822 can be exluded and calls with more than one arg get a separate C812 error code and can be left on:

logger.info(
    'log message',
    extra={'extra': 'data'}  # C812 missing trailing comma in enclosure
)

This also adds separate codes for function definitions and single element collections.

We've had many production failures due to inadvertently having trailing commas on a line, resulting in a tuple where the single object was expected.

I'd like a way to check for bare trailing commas. This PR reuses the existing C819 error for this case, but I'm open to creating a new error code for it.

I've added support for identifying multi-line list and dict comprehensions.

This is implemented with a simple stack to track the current bracket context and whether that is for a list/dict comprehension (identified with the for token), which means that it still identifies missing trailing commas in non-comprehension structures that are within comprehensions.

This fixes #3

This fixes the extension for flake8>=3, issue #20. I just followed the convention in the documentation: http://flake8.readthedocs.io/en/latest/plugin-development/registering-plugins.html

Tried it with both flake8 2.6.2 & 3.0.4 - works in both.

When I prepared requirements file:

# flake8
flake8==2.5.4
mccabe==0.4.0
pep8==1.7.0
pyflakes==1.0.0

# flake8 extensions
flake8-blind-except==0.1.0
flake8-debugger==1.4.0
flake8-pep257==1.0.5
flake8-print==2.0.1
flake8-quotes==0.1.2
flake8-string-format==0.2.1
flake8-commas==0.1.1
flake8-import-order==0.6.1
flake8-pep3101==0.2
pep8-naming==0.3.3

Then run pip install -r../requirements.dev.txt

And got this:

Collecting flake8-commas==0.1.1 (from -r ../requirements.txt (line 55))
  Using cached flake8-commas-0.1.1.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/tmp/pip-build-VIomAr/flake8-commas/setup.py", line 3, in <module>
        import flake8_commas
      File "/tmp/pip-build-VIomAr/flake8-commas/flake8_commas.py", line 3, in <module>
        import pep8
    ImportError: No module named pep8

I think it's better to update version in setup.py in similar way as in flake8_commas.py.

Hope to see the new version (0.1.2) soon (: Thanks for extension!

Is it possible to not require trailing commas on multiline function/method calls? At the moment they're getting flagged with C812, which we want for the other multiline errors, just not for function and method calls.

Ideally if the error code for function and method calls was different than C812 we could make our own exceptions for those in our flake8 config.

I think flake8-commas is getting confused between python 3's print function and python 2's print statement followed by a concatenated string literal.

This is valid python code:

print (
    "abcdefghijklmnopqrstuvwxyz"
    "zyxwvutsrqponmlkjihgfedcba"
)

see: https://docs.python.org/2/reference/lexical_analysis.html#string-literal-concatenation

It is equivalent to:

print "abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba"

However, Flake8-commas produces the warning:

C813 missing trailing comma in Python 3

Adding a trailing comma to the end of the concatenated string literal turns the statement into a tuple. Equivalent to this:

print ("abcdefghijklmnopqrstuvwxyzzyxwvutsrqponmlkjihgfedcba", )

Which is not the same thing.

Updated*

Traceback (most recent call last):
  File "venv/bin/flake8", line 11, in <module>
    sys.exit(main())
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/main/cli.py", line 16, in main
    app.run(argv)
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/main/application.py", line 322, in run
    self._run(argv)
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/main/application.py", line 306, in _run
    self.run_checks()
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/main/application.py", line 244, in run_checks
    self.file_checker_manager.run()
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/checker.py", line 350, in run
    self.run_serial()
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/checker.py", line 334, in run_serial
    checker.run_checks(self.results_queue, self.statistics_queue)
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/checker.py", line 606, in run_checks
    self.run_ast_checks()
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8/checker.py", line 517, in run_ast_checks
    for (line_number, offset, text, check) in runner:
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8_commas/_base.py", line 262, in run
    for error in get_comma_errors(tokens):
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8_commas/_base.py", line 198, in get_comma_errors
    for token in tokens:
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8_commas/_base.py", line 122, in simple_tokens
    token = next(tokens)
  File "/home/johny/work/result-api/venv/local/lib/python2.7/site-packages/flake8_commas/_base.py", line 120, in <genexpr>
    tokens = (t for t in tokens if t.type != tokenize.COMMENT)

tokens are not fed into the Token class when they are passed as file_tokens parameter in the CommaChecker class. Any check to the Token class properties will create an error. This PR fixes these errors.

In at least Python 3.5 and above it's valid to do:

result = function(
    foo,
    bar,
    *args,
    more,
)

This also works for tuple & list literals (and possibly elsewhere).

It would be great if flake8-commas could require a comma in such places when one is missing:

result = function(
    foo,
    bar,
    *args
)
tpl = (
    foo,
    bar,
    *args
)
lst = [
    foo,
    bar,
    *args
]

There is the following code:

print(
    'too long line'
    ' second part'
    ' last part'
     )

It uses https://docs.python.org/3/reference/lexical_analysis.html#string-literal-concatenation feature to split long lines. This code is correct based on regular flake8 checks.

But it raises print.py:4:17: C813 missing trailing comma in Python 3 error.

My expectation that it has to pass flake8-commas rules also, hasn't it?

If a function argument contains multiplication, a C815 error ("... in Python 3.5+") is reported instead of C812, as if the expression includes tuple unpacking. This is misleading, because even Python 2.7 supports a trailing comma after multiplication.

Example Code

def foo(x): pass

foo(
    1
)
foo(
    *(1,)
)
foo(
    2 * 1
)

Actual Behavior

$ flake8 --select=C812,C815 repr.py
repr.py:4:6: C812 missing trailing comma
repr.py:7:10: C815 missing trailing comma in Python 3.5+
repr.py:10:10: C815 missing trailing comma in Python 3.5+

Expected Behavior

I would expect the error reported for line 10 to be C812, not C815.

Software Versions

Python 3.9 flake8-commas 2.0.0

Currently both tox.ini and travis.yml do not support latest python versions.

I can send a PR with the fix!

Related: https://github.com/wemake-services/wemake-python-styleguide/issues/1138

I'd like to ignore the error when there's only one argument to the function. For example:

logger.debug(
    "Really long string "
    "implicitly joined"
)

I'd like to ignore the enforcement of a trailing comma where all items are on a single line that isn't the same line as the opening bracket. For example,

long_function_name(
    argument1, argument2, keyword=argument3
)