Why doesn't Python 2.6 have set literals and comprehensions or dict comprehensions?

Question

Python 2.6 was basically a stepping stone to make converting to Python 3 easier. A lot of the features destined for Python 3 were implemented in 2.6 if they didn't break backward compatibility with syntax and the class libs.

Why weren't set literals ({1, 2, 3}), set comprehensions ({v for v in l}), or dict comprehensions ({k: v for k, v in d}) among them? In particular dict comprehensions would have been a great boon... I find myself using the considerably uglier dict([(k, v) for k, v in d]) an awful lot lately.

Is there something obvious I'm missing, or was this just a feature that didn't make the cut?

Answer 1

All these are syntax/grammar changes. Such changes are traditionally introduced first in a Python x.y version with a from __future__ import … statement, and implemented at least on Python x.(y+1) version. Such a transition hasn't happened yet for these changes.

Technically, I've answered your "why".

Now, if you meant, “why didn't anyone take the time to suggest, support and implement something that I would like to have in 2.x also, even if they don't know about it since I never tried to suggest/support backporting those syntax enhancements in either comp.lang.python or Python-Dev and I never tried to even read the PEPs?”, then the answer lies in you too, and you can offer an answer yourself.

HTH

BTW, you shouldn't use the dict([(k,v) for k,v in d]) form, but the dict((k,v) for k,v in d). More efficient. Why create an intermediate list?

Answer 2

It wasn't done because nobody took the time to do it. There are bugs opened for months, and no one commented on them:

http://bugs.python.org/issue2333 http://bugs.python.org/issue2334 http://bugs.python.org/issue2335

So it wasn't important enough for anybody to care, probably.