[Python-Dev] PEP 408 -- Standard library preview package (original) (raw)

Eli Bendersky eliben at gmail.com
Sat Jan 28 04:11:14 CET 2012

No, potentially wrong in cases where the APIs are different. Even with the try...except ImportError dance around StringIO / cStringIO there are some API differences. But for a lot of use cases it works fine (simplejson and json aren't identical, but it works for most people).

Okay, granted, I accept your point. But I think we need to distinguish between these cases. In the case of StringIO and cStringIO, API compatibility is expected, and differences are either bugs or implementation differences that you shouldn't be relying on.

I just recently ran into a compatibility of StringIO and cStringIO. It's a good thing it's documented:

"Another difference from the StringIO module is that calling StringIO() with a string parameter creates a read-only object. Unlike an object created without a string parameter, it does not have write methods. These objects are not generally visible. They turn up in tracebacks as StringI and StringO."

But it did cause me a couple of minutes of grief until I found this piece in the docs and wrote a work-around. But no, even in the current stable stdlib, the "try import ... except import from elsewhere" trick doesn't "just work" for StringIO/cStringIO. And as far as I can understand this is documented, not a bug or some obscure implementation detail.

My point is that if our users accept this, in the stable stdlib, I see no reason they won't accept the same happening between preview and a graduated module, when they (hopefully) understand the intention of preview.

Eli

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