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https://github.com/asottile/add-trailing-comma

A tool (and pre-commit hook) to automatically add trailing commas to calls and literals.
https://github.com/asottile/add-trailing-comma

linter pre-commit python

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

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add-trailing-comma
==================

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

## Installation

```bash
pip install add-trailing-comma
```

## As a pre-commit hook

See [pre-commit](https://github.com/pre-commit/pre-commit) for instructions

Sample `.pre-commit-config.yaml`:

```yaml
- repo: https://github.com/asottile/add-trailing-comma
rev: v3.1.0
hooks:
- id: add-trailing-comma
```

## multi-line method invocation style -- why?

```python
# 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:

```python
# 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:

```diff
# with no trailing commas
x(
- arg
+ arg,
+ arg2
)
```

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

## Implemented features

### trailing commas for function calls

```diff
x(
arg,
- arg
+ arg,
)
```

### trailing commas for tuple / list / dict / set literals

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

### trailing commas for function definitions

```diff
def func(
arg1,
- arg2
+ arg2,
):
```

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

### trailing commas for `from` imports

```diff
from os import (
path,
- makedirs
+ makedirs,
)
```

### trailing comma for class definitions

```diff
class C(
Base1,
- Base2
+ Base2,
):
pass
```

### trailing comma for with statement

```diff
with (
open('f1', 'r') as f1,
- open('f2', 'w') as f2
+ open('f2', 'w') as f2,
):
pass
```

### trailing comma for match statement

```diff
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

```diff
def f[
- T
+ T,
](x: T) -> T:
return x
```

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

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

### unhug trailing paren

```diff
x(
arg1,
- arg2)
+ arg2,
+)
```

### unhug leading paren

```diff
-function_name(arg1,
- arg2)
+function_name(
+ arg1,
+ arg2,
+)
```

### match closing brace indentation

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

### remove unnecessary commas

yes yes, I realize the tool is called `add-trailing-comma` :laughing:

```diff
-[1, 2, 3,]
-[1, 2, 3, ]
+[1, 2, 3]
+[1, 2, 3]
```