removing list comprehensions in Python 3.0

[Raymond Hettinger]

[Raymond Hettinger]
> > It is darned inconvenient to get an iterator when you really
> > need a list, when you want to slice the result, when you want to see a
> > few elements through repr(), and when you need to loop over the
> > contents more than once.

[George Sakkis]
> Similar arguments can be given for dict comprehensions as well.

You'll find that "lever" arguments carry little weight in Python
language design (well, you did X in place Y so now you have to do it
everywhere even if place Z lacks compelling use cases).

For each variant, the balance is different.  Yes, of course, list
comprehensions have pros and cons similar to set comprehensions, dict
comps, etc.  However, there are marked differences in frequency of use
cases, desirability of having an expanded form, implementation issues,
varying degrees of convenience, etc.

The utility and generality of genexps raises the bar quite high for
these other forms.  They would need to be darned frequent and have a
superb performance advantage.

Take it from the set() and deque() guy, we need set, dict, and deque
comprehensions like we need a hole in the head.  The constructor with a
genexp does the trick just fine.

Why the balance tips the other way for list comps is both subjective
and subtle.  I don't expect to convince you by a newsgroup post.
Rather, I can communicate how one of the core developers perceives the
issue.  IMHO, the current design strikes an optimal balance.

'nuff said,


Raymond