Trailing comma for function which enforces keyword arguments (`f(*, a, b, ...)`)

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 😄

[asottile]

black absolutely does?

def f(
    this,
    function,
    has,
    a,
    whole,
    bunch,
    of,
    parameters,
    but,
    theres,
    no,
    trailing,
    comma
):
    pass

$ venv39/bin/black --diff t2.py 
--- t2.py	2021-05-27 15:45:24.778542 +0000
+++ t2.py	2021-05-27 15:45:26.187483 +0000
@@ -9,8 +9,8 @@
     parameters,
     but,
     theres,
     no,
     trailing,
-    comma
+    comma,
 ):
     pass
would reformat t2.py
All done! ✨ 🍰 ✨
1 file would be reformatted

[asottile]

you don’t actually want that, trust me. you’d end up with this ugly nonsense

-class C(A): pass
-
-f(1)
+class C(
+    A,
+): pass
+
+f(
+    1,
+)