[Python-ideas] Globalize lonely augmented assignment

[Georg Brandl]

Am 12.06.2010 17:43, schrieb Bruce Frederiksen:

> So we are considering the case where no assignment to the variable
> exists within the function, but there is an augmented assignment.  But
> in this case, if we say that the variable is a local variable, how did
> this local variable get a value that the augmented assignment can then
> use?
> 
> The only way that I can think of is:
> 
> def foo():
>     def bar():
>         nonlocal A
>         A = []
>     bar()
>     A += [2]

(I assume you intended a global A somewhere outside of foo().)
With the proposed semantics, this would actually be a compilation error,
since there is no nonlocal binding of A that the "nonlocal" statement
could bring into scope.

> What am I missing?

Currently, augmented assignment has a very straightforward translation to
plain assignment::

   a += b   is equivalent to
   a = a.__iadd__(b)

(Not just ``a.__iadd__(b)``, as some people think at first.  That's a
problem, see below.)

With the proposal, it would be much more complicated and dependent on
the context: "... it's the same as <code>, but if the name would only
be made a local by augmented assignment statements, it's automatically
made nonlocal if there's a matching non-local binding, or global
otherwise."  Pretty scary.  And while I think about it, it's pretty
implicit as well, since it basically makes a global or nonlocal binding
(this would be different if the translation didn't include the actual
assignment).

Georg

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