[Python-Dev] redefining is (original) (raw)

Phillip J. Eby pje at telecommunity.com
Fri Mar 19 17:57:09 EST 2004

At 05:40 PM 3/19/04 -0500, Andrew Koenig wrote:

Nevertheless, I still wish that expressions such as "x is 'foo'" did not silently differ in outcome from one implementation to another.

The part that drives me nuts about this discussion is that in my view, "x is 'foo'" has the same outcome on all implementations. That is, it's true if x refers to that exact string object.

The thing that's different from one implementation to the next is whether there's any chance in hell of x being that same 'foo' string. But to me, that 'foo' string looks like a newly created string, so to the naive glance there's no possible way that it could be the same object. In other words, it looks like a bad expression to use in the first place: one that's guaranteed to be false, except by accident of implementation.

So, I have trouble understanding how it is that somebody could get to a place where they think that using 'is' for strings and numbers is a good idea in the first place. But then, I read the entire Python language reference (and a good chunk of the library reference) before I tried writing even a single line of Python code, so I can imagine that my perspective on this might not be the most common one. :)

More information about the Python-Dev mailing list