[Python-ideas] Should this be considered a bug?

[Nick Coghlan]

On Sun, Oct 30, 2011 at 9:10 PM, Georg Brandl <g.brandl at gmx.net> wrote:
> It's still a bit inconsistent though (e.g. it doesn't work with tuple's
> __iadd__).

Tuple doesn't have an __iadd__, it's immutable :)

As Antoine noted, list.__iadd__ is actually just list.extend under the
hood, and accepts an arbitrary iterable.

We're a bit more restrictive with other mutable container types (e.g.
set, bytearray), but in those cases, the corresponding methods also
only accept a limited selection of object types.

(There's also a longstanding limitation in the type coercion system
where returning NotImplemented doesn't work properly for the sequence
slots at the C level - you have to use the numeric slots instead. That
issue should finally be resolved in 3.3)

> Also, "type stays the same" is not true in other instances, e.g.
>
> i = 1
> i += 0.5

Again, that's an immutable type, and the various numeric types go to
great lengths in order to play nicely together and negotiate the
"correct" result type. Even there, we deliberately complain when we
think something dodgy might be going on:

>>> import decimal
>>> decimal.Decimal(1) + 1.0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'Decimal' and 'float'

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia