Strange location for a comma

[Peter Otten]

ast wrote:

> 
> "ast" <nomail at invalid.com> a écrit dans le message de
> news:55e83afb$0$3157$426a74cc at news.free.fr...
>> Hello,
>> At the end of the last line of the following program,
>> there is a comma, I dont understand why ?
>>
>> Thx
>>
>>
>> from cx_Freeze import setup, Executable
>>
>> # On appelle la fonction setup
>> setup(
>>    name = "salut",
>>    version = "0.1",
>>    description = "Ce programme vous dit bonjour",
>>    executables = [Executable("salut.py")],    #  <--- HERE
>> )
>>
>>
> 
> Ok its understood, it's a 1 element only tuple
> 
> example:
> 
>>>> A = 5,
>>>> A
> (5,)
> 
>>>> A = (6)
>>>> A
> 6
> 

No, in a function call an extra comma has no effect:

>>> def f(x): return x
... 
>>> f(42)
42
>>> f(42,)
42
>>> f(x=42)
42
>>> f(x=42,)
42

The only reason I see to add an extra comma are smaller and easier to read 
diffs when you make a change:

$ cat before.py
func(
    arg_one=1,
    arg_two=2
)

func(
    arg_one=1,
    arg_two=2,
)
$ cat after.py
func(
    arg_one=1,
    arg_two=2,
    arg_three=3
)

func(
    arg_one=1,
    arg_two=2,
    arg_three=3,
)
$ diff -u before.py after.py
--- before.py   2015-09-03 14:44:27.709735075 +0200
+++ after.py    2015-09-03 14:44:55.275958331 +0200
@@ -1,9 +1,11 @@
 func(
     arg_one=1,
-    arg_two=2
+    arg_two=2,
+    arg_three=3
 )
 
 func(
     arg_one=1,
     arg_two=2,
+    arg_three=3,
 )