[Python-Dev] INPLACE_ADD and INPLACE_MULTIPLY oddities in ceval.c (original) (raw)

Armin Rigo arigo at tunes.org
Thu Mar 30 09:27:02 CEST 2006

Hi Tim,

On Wed, Mar 29, 2006 at 08:45:10AM -0700, Tim Hochberg wrote:

Ouch. Assuming the same path is followed with tuples, I think that this means the following behaviour will continue:

>>> t = (1,2,3) >>> a = array([4,5,6]) >>> t += a >>> t array([5, 7, 9])

I fell into the same trap at first, but no: in fact, only lists have a special in-place addition among all the built-in objects. Tuples fall back to the normal addition, which means that you can only add tuples to tuples:

>>> t = (1,2,3)
>>> t += [4,5,6]
TypeError: can only concatenate tuple (not "list") to tuple

>>> t += array([4,5,6])
TypeError: ...

This is current behavior and it wouldn't change.

A bientot,

Armin.

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