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

[Guido van Rossum]

On 8/9/06, Georg Brandl <g.brandl at gmx.net> wrote:
> Terry Reedy wrote:
> > "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.
>
> This is similar to
>
> x = ([1], 2)
> x[0] += [2]
>
> which doesn't currently work either, though it could.

No it couldn't. You can't assign to x[0]. L += R is defined as L =
L.__iadd__(R) so L must be a valid assignment target.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)