[Tutor] When are strings interned?

[Jeremiah Dodds]

On Wed, Jul 1, 2009 at 4:44 PM, Angus Rodgers <angusr at bigfoot.com> wrote:

> Hello, world!
>
> This is my first post to the Tutor list (although I've already
> posted to comp.lang.python a couple of times).
>
> I'm currently reading Chapter 4 of Wesley Chun's book, "Core
> Python Programming" (2nd ed.).
>
> I find this, in Python 2.5.4, on my Win98SE system (using IDLE):
>
> >>> n = "colourless"
> >>> o = "colourless"
> >>> n == o
> True
> >>> n is o
> True
> >>> p = "green ideas"
> >>> q = "green ideas"
> >>> p == q
> True
> >>> p is q
> False
>
> Why the difference?
> --
>
>

IIRC, in cPython (the "defaul" python available from python.org), there is
an optimization done for strings (and I think integers) below a certain
size. This is an implementation detail, and could be different in (for
instance) Jython.
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