[Python-Dev] SyntaxError: can't assign to function call

[Terry Reedy]

"Neal Becker" <ndbecker2 at gmail.com> wrote in message 
news:ebd2sp$nnv$1 at sea.gmane.org...
> class X (object):
>    pass
>
> X() += 2
>
>> SyntaxError: can't assign to function call
>
> Suppose I actually had defined __iadd__ for class X.  Python says this
> syntax is invalid.  I wish is wasn't.

If you translate to x() = x() +2, with x called just once, it does not make 
sense.  You can bind to names and slots in compound objects, but not to 
objects.

> Here's where I might use it.  Suppose I have a container class.  Suppose 
> I
> could make a slice of this container, like so:
>
> c = Container()
> s = Slice (c, 0, 10)
>
> where "Slice" is a class.  Then:
>
> s += 2
>
> Would perform iadd on the slice of the container.  A convenient syntax 
> would
> be:
>
> Slice (c, 0, 10) += 2

If this were made to work, the unbound object you are making an 
'assignment' to, purely for side effect, would disappear.  So if you don't 
want a separate object to be named and kept around, give your container a 
sliceadd method:
c.sliceadd((0,10), 2)

>
> Does anyone else think this would be a good addition to Python?

I don't.  Augmented assigment is confusing enough to many.

Terry Jan Reedy