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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: v2.4.0
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 function calls with unpackings
If `--py35-plus` is passed, `add-trailing-comma` will also perform the
following change:
```diff
x(
- *args
+ *args,
)
y(
- **kwargs
+ **kwargs,
)
```
Note that this would cause a **`SyntaxError`** in earlier python versions.
### 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 function definitions with unpacking arguments
If `--py36-plus` is passed, `add-trailing-comma` will also perform the
following change:
```diff
def f(
- *args
+ *args,
): pass
def g(
- **kwargs
+ **kwargs,
): pass
def h(
- *, kw=1
+ *, kw=1,
): pass
```
Note that this would cause a **`SyntaxError`** in earlier python versions.
### 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
```
### 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]
```