[Python-Dev] [Python-3000] Warning for 2.6 and greater (original) (raw)

Guido van Rossum guido at python.org
Fri Jan 12 20:24:47 CET 2007

On 1/12/07, Steven Bethard <steven.bethard at gmail.com> wrote:

Yeah, when this was talked about last time, I wrote PEP 3002 which requests exactly this:

http://www.python.org/dev/peps/pep-3002/ It basically proposes that all backwards-incompatible changes be discussed in a PEP somewhere, and that code like Anthony's be added to 2.X to ease the transition. Originally, it has proposed just a utility like Guido's 2to3 but Guido himself suggested something like Anthony's approach: http://mail.python.org/pipermail/python-3000/2006-April/001444.html

To complement 2to3, not to replace it.

I'm planning to update the PEP with any new conclusions arrived at in this thread.

I think that now the 2to3 tool is a reality, its limitations should perhaps be taken into account.

For example, I don't believe it is realistic to expect it to do semantic analysis, which means that for example it can't be expected to know whether 'd' in 'd.keys()' is a dict or something else.

Also, in 'k = d.keys()' it can't be expected to analyze how k is used later on; to be safe, it will translate all occurrences of d.keys() into list(d.keys()) which is known to work (and won't be slower than the original code either).

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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