var or inout parm?

[Steve Holden]

sturlamolden wrote:
> On Dec 12, 3:08 pm, Marc 'BlackJack' Rintsch <bj_... at gmx.net> wrote:
> 
>> No bug because a mutation *is* attempted.  ``a += x`` calls `a.__iadd__`
>> which *always* returns the result which is *always* rebound to the name
>> `a`.  Even with mutable objects where `__iadd__()` simply returns
>> `self`!
> 
> No, a mutation is not attempted, even if __iadd__() always returns a
> value. If a rebinding of a member to the same member is attempted, the
> tuple should not raise an exception. The tuple should check that it is
> actually being *mutated* before it raises any exception. There is an
> attempted write to the tuple, but not an attempted mutation of the
> tuple. The tuple should tell the difference. Immutability does not
> imply inwriteability, if the write operation changes nothing. But the
> tuple raises an exception on any write attempt.
> 
OK, so if you regard the current behavior as a bug explain how to modify
the tuple's __iadd__ method and the coding of the INPLACE_ADD operator.
At least in pseudocode.

Criticism is easy. Now demonstrate that it's *informed* criticism.
Enough of the "should". I am always suspicious of suggestions that say
what the interpreter "should" or "should not" do. It makes it sound as
though you can wave a magic wand to achieve the desired behavior.

The interpreter "should not" have a GIL. The tuple "should" check that
it is actually being mutated. How?

regards
 Steve
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