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Description:

addtrailingcomma 3.1.0

add-trailing-comma
A tool (and pre-commit hook) to automatically add trailing commas to calls and
literals.
Installation
pip install add-trailing-comma

As a pre-commit hook
See pre-commit for instructions
Sample .pre-commit-config.yaml:
- repo: https://github.com/asottile/add-trailing-comma
rev: v3.1.0
hooks:
- id: add-trailing-comma

multi-line method invocation style -- why?
# Sample of *ideal* syntax
function_call(
argument,
5 ** 5,
kwarg=foo,
)

the initial paren is at the end of the line
each argument is indented one level further than the function name
the last parameter (unless the call contains an unpacking
(*args / **kwargs)) has a trailing comma

This has the following benefits:

arbitrary indentation is avoided:
# I hear you like 15 space indents
# oh your function name changed? guess you get to reindent :)
very_long_call(arg,
arg,
arg)

adding / removing a parameter preserves git blame and is a minimal diff:
# with no trailing commas
x(
- arg
+ arg,
+ arg2
)

# with trailing commas
x(
arg,
+ arg2,
)

Implemented features
trailing commas for function calls
x(
arg,
- arg
+ arg,
)

trailing commas for tuple / list / dict / set literals
x = [
- 1, 2, 3
+ 1, 2, 3,
]

trailing commas for function definitions
def func(
arg1,
- arg2
+ arg2,
):

async def func(
arg1,
- arg2
+ arg2,
):

trailing commas for from imports
from os import (
path,
- makedirs
+ makedirs,
)

trailing comma for class definitions
class C(
Base1,
- Base2
+ Base2,
):
pass

trailing comma for with statement
with (
open('f1', 'r') as f1,
- open('f2', 'w') as f2
+ open('f2', 'w') as f2,
):
pass

trailing comma for match statement
match x:
case A(
1,
- 2
+ 2,
):
pass
case (
1,
- 2
+ 2,
):
pass
case [
1,
- 2
+ 2,
]:
pass
case {
'x': 1,
- 'y': 2
+ 'y': 2,
}:
pass

trailling comma for PEP-695 type aliases
def f[
- T
+ T,
](x: T) -> T:
return x

class A[
- K
+ K,
]:
def __init__(self, x: T) -> None:
self.x = x

type ListOrSet[
- T
+ T,
] = list[T] | set[T]

unhug trailing paren
x(
arg1,
- arg2)
+ arg2,
+)

unhug leading paren
-function_name(arg1,
- arg2)
+function_name(
+ arg1,
+ arg2,
+)

match closing brace indentation
x = [
1,
2,
3,
- ]
+]

remove unnecessary commas
yes yes, I realize the tool is called add-trailing-comma :laughing:
-[1, 2, 3,]
-[1, 2, 3, ]
+[1, 2, 3]
+[1, 2, 3]