if (foo and
    bar()):
    pass

I expect to be rewritten to

if (
    foo and
    bar()
):
    pass

But I imagine the same code that prevents this from being rewritten is firing:

foo('bar {}'.format(
    'baz',
))

which I don't think should be rewritten.

Need to come up with a more clever heuristic here.

I think the following would be some good enhancements to this tool:

• --diff like isort, which prints the suggested changes on stdout, instead of modifying the files.

  This is great for CI checks where a contributor gets to see the required changes to fix the situation directly.

• --recursive option, to specify an entire project directory without globs.

  This would make CLI invocations easier.

I'll be happy to write PRs for them if @asottile thinks they're reasonable.

I have some code that black formatted like this actual

            extended_retry_message = textwrap.dedent(
                f"""\
                {retry_message[0]}
                {retry_blurb}
            """
            )  # noqa: N400

expected

            extended_retry_message = textwrap.dedent(
                f"""\
                {retry_message[0]}
                {retry_blurb}
            """,
            )  # noqa: N400

another actual

                        assert all(
                            (
                                v == result["new_expectations"][k]
                                for k, v in {
                                    "jenkins_id": jn.jenkins_id,
                                }.items()
                            )
                        )

expected

                        assert all(
                            (
                                v == result["new_expectations"][k]
                                for k, v in {
                                    "jenkins_id": jn.jenkins_id,
                                }.items()
                            ),
                        )

i have add-trailing-comma running right after black with --py36-plus and it doesnt add the trailing comma to that function call

 -   repo: https://github.com/asottile/add-trailing-comma
     rev: v2.2.1
     hooks:
     -   id: add-trailing-comma
         args: [--py36-plus]

Didn't initially realise that args had to be on separate lines for functions in order for add-trailing-comma to modify (in original comment). Realised that and added to # edit.

original comment

# requirements.txt
appdirs==1.4.4
cfgv==3.3.0
distlib==0.3.1
filelock==3.0.12
identify==2.2.6
nodeenv==1.6.0
pre-commit==2.13.0
PyYAML==5.4.1
six==1.16.0
toml==0.10.2
virtualenv==20.4.7

#.pre-commit-config.yaml 
minimum_pre_commit_version: 2.10.0
repos:
  - repo: https://github.com/asottile/add-trailing-comma
    rev: v2.1.0
    hooks:
      - id: add-trailing-comma
        args: [--py36-plus]

Running pre-commit as: pre-commit run --all-files I'm expecting (hoping...) with the following test file:

def A(*, a):
    return True

def B(a,b):
    return True

def C(*args):
    return True

x = [1, 2, 3]

def function_call(a, b, c):
    return True 

function_call(
    a=1, b=2, c=3
)

Gives the diff:

diff --git a/test.py b/test.py
index 6bc7d22..edf345f 100644
--- a/test.py
+++ b/test.py
@@ -13,5 +13,5 @@ def function_call(a, b, c):
     return True

 function_call(
-    a=1, b=2, c=3
+    a=1, b=2, c=3,
 )

Though the diff that I was expecting (...hoping?) for was:

diff --git a/test.py b/test.py
index 6bc7d22..768e441 100644
--- a/test.py
+++ b/test.py
@@ -1,17 +1,17 @@
-def A(*, a):
+def A(*, a,):
     return True

-def B(a,b):
+def B(a,b,):
     return True

-def C(*args):
+def C(*args,):
     return True

-x = [1, 2, 3]
+x = [1, 2, 3,]

-def function_call(a, b, c):
+def function_call(a, b, c,):
     return True

 function_call(
-    a=1, b=2, c=3
+    a=1, b=2, c=3,
 )

There's probably something that I'm missing - but having looked through the readme I'm not sure what.

edit

Given the following file:

def A(*, 
a):
    return True

def B(a,
b):
    return True

def C(*args
):
    return True

x = [1, 2, 3]

def function_call(a, b, 
c):
    return True 

function_call(
    a=1, b=2, c=3
)

the diff is as expected having run : pre-commit run --all-files:

diff --git a/test.py b/test.py
index f37eb5c..361e427 100644
--- a/test.py
+++ b/test.py
@@ -1,21 +1,28 @@
-def A(*,
-a):
+def A(
+    *,
+    a,
+):
     return True

-def B(a,
-b):
+def B(
+    a,
+    b,
+):
     return True

-def C(*args
+def C(
+    *args,
 ):
     return True

 x = [1, 2, 3]

-def function_call(a, b,
-c):
+def function_call(
+    a, b,
+    c,
+):
     return True

 function_call(
-    a=1, b=2, c=3
+    a=1, b=2, c=3,
 )

Seems I didn't realise that they had to be on separate lines in order for add-trailing-comma to pick up on them.

If there's a way to set this so that add-trailing-comma added a trailing comma to functions all the time that would be ideal.

If not then this may have shifted from an issue to a feature request and can probably be closed 😄

I ran into the following error when committing: VSCode console output:

> git -c user.useConfigOnly=true commit --quiet --allow-empty-message --file -
Trim Trailing Whitespace.................................................Passed
Fix End of Files.........................................................Passed
Check docstring is first.................................................Passed
Debug Statements (Python)................................................Passed
Fix requirements.txt.................................(no files to check)Skipped
Check for added large files..............................................Passed
Check python ast.........................................................Passed
Check builtin type constructor use.......................................Passed
Check for case conflicts.................................................Passed
Detect Destroyed Symlinks................................................Passed
Check for merge conflicts................................................Passed
Check Yaml...........................................(no files to check)Skipped
Debug Statements (Python)................................................Passed
Detect Private Key.......................................................Passed
fix UTF-8 byte order marker..............................................Passed
Add trailing commas......................................................Failed
- hook id: add-trailing-comma
- exit code: 1

Traceback (most recent call last):
  File "c:\program files\python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "c:\program files\python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\navdh\.cache\pre-commit\repoy6phnb7j\py_env-python3.9\Scripts\add-trailing-comma.EXE\__main__.py", line 7, in <module>
  File "c:\users\navdh\.cache\pre-commit\repoy6phnb7j\py_env-python3.9\lib\site-packages\add_trailing_comma.py", line 498, in main
    ret |= fix_file(filename, args)
  File "c:\users\navdh\.cache\pre-commit\repoy6phnb7j\py_env-python3.9\lib\site-packages\add_trailing_comma.py", line 470, in fix_file
    contents_text = _fix_src(contents_text, args.py35_plus, args.py36_plus)
  File "c:\users\navdh\.cache\pre-commit\repoy6phnb7j\py_env-python3.9\lib\site-packages\add_trailing_comma.py", line 401, in _fix_src
    tokens, _find_call(call, i, tokens),
  File "c:\users\navdh\.cache\pre-commit\repoy6phnb7j\py_env-python3.9\lib\site-packages\add_trailing_comma.py", line 239, in _find_call
    raise AssertionError('Past end?')
AssertionError: Past end?```

Platform: Windows 10 21H1 OS Build 19043.906
Python Version: 3.9.1

My config:

repos:
    - repo: https://github.com/pre-commit/pre-commit-hooks
      rev: v3.4.0
      hooks:
          - id: trailing-whitespace
          - id: end-of-file-fixer
          - id: check-docstring-first
          - id: debug-statements
          - id: requirements-txt-fixer
          - id: check-added-large-files
          - id: check-ast
          - id: check-builtin-literals
          - id: check-case-conflict
          - id: destroyed-symlinks
          - id: check-merge-conflict
          - id: check-yaml
          - id: debug-statements
          - id: detect-private-key
          - id: fix-byte-order-marker
    - repo: https://github.com/asottile/add-trailing-comma
      rev: v2.0.1
      hooks:
          - id: add-trailing-comma
            args: [--py36-plus]

Tools like ALE and so forth generally pass the buffer of the editor directly to the tool to edit and expect to read it back on stdout. I've added the - to signal to add-trailing-comma to read data from stdin and output to stdout. Note: this is why I always output the text, regardless of whether it changed. ALE would just wipe the buffer if add-trailing-comma returned nothing.

I modeled this mostly off of tools like black and isort. Black doesn't have any error handling around passing multiple files and -. Black also only briefly mentions it in the docs.

I've also added two basic tests to check that a (mocked) stdin works.

Previously, since the file was opened as bytes but written as text, \r\n got written as \r\r\n, since it read in \r\n as bytes, passed through the \r, then wrote out \r\n as text, which using Python's universal newline support automatically transforms \n into \r\n on Windows, resulting in \r\r\n. Thus, this was adding bunches of \r characters every time it was run. This PR fixes that.

We are using add-trailing-comma for dangling commas and isort to keep our imports organized. Ideally, both can run as pre-commit hooks. However, the two tools clash on statements like this:

from my_library.api.database.models import (Model1, Model2, Model3, Model4, Model5, Model6
                                            Model7,)

where isort prefers this style and add-trailing-comma reformats it into:

from my_library.api.database.models import (
    Model1, Model2, Model3, Model4, Model5, Model6
    Model7,
)

When trying to commit, no matter the order between isort and add-trailing-comma, the imports are always re-arranged, preventing commit. Disabling add-trailing-comma on imports would allow us to run isort and to use your tool for other parts of the file.

Before add-trailing-comma

def g(dict_representation):
    assert (
        set(dict_representation["cli"].pop("characteristics")
            ) == set(cli_data.pop("characteristics"))
    )

after add-trailing-comma

def g(dict_representation):
    assert (
        set(
            dict_representation["cli"].pop("characteristics"), # there should not be any comma, because set() gets only one parameter
        ) == set(cli_data.pop("characteristics"))
    )

Create a test.py:

# -*- coding: utf-8 -*-

test = [
    1,
    2
]

add-trailing-comma - < test.py outputs correctly:

# -*- coding: utf-8 -*-

test = [
    1,
    2,
]

But the return statuscode is 1:

❯ echo $?                                                                                                                                                   [11:30:11]
1

This is a different behavior from other formatters, like black:

black - < test.py                                                                                                                                         [11:30:46]
# -*- coding: utf-8 -*-

test = [1, 2]
reformatted -
All done! ✨ 🍰 ✨
1 file reformatted.
 ❯ echo $?                                                                                                                                                   [11:30:54]
0

Some formatters in editors (like vim-autoformat) expect a 0 statuscode to make sure the formatter call was ok, and this is inconsistent with exit codes with special meanings.

Since the stdin feature comes from a month old PR (https://github.com/asottile/add-trailing-comma/pull/75), I think it's nice to consider changing this to be standard like other tools.

Hey @asottile ; I am trying to use add-trailing-comma as part of formatting and use flake8-comma as check against it. I can see this as help:

usage: add-trailing-comma [-h] [--exit-zero-even-if-changed] [--py35-plus] [--py36-plus] [filenames ...]

My understanding is the directory option is not currently available. I have seen black or isort have this ability:

  --src SRC_PATHS, --src-path SRC_PATHS
                        Add an explicitly defined source path (modules within src paths have their imports automatically categorized as first_party). Glob expansion (`*` and `**`) is supported for
                        this option.

I was wondering maybe this can be a very helpful feature. I also appreciate it if you direct me how can I apply this on a directory. For example, lets say I have src/ and tests/ and I wanna apply add-trailing-comma to all .py files. Currently, I am running the snippet below (I use poetry) in my formatting scripts:

poetry run add-trailing-comma src/**/*.py tests/**/*.py