RE: What do list comprehensions do that generator expressions don't?
Mark English
> From: Mike Meyer <m...@mired.org>
> Which means that the real rule should be always use generator
expressions,
> unless you *know* the expression will always fit in memory.
> Which leads to the obvious question of why the exception.
<code>
>>> l = [(1, 2), ('a', 'b'), (3, 2), (23, 32)]
>>> l
[(1, 2), ('a', 'b'), (3, 2), (23, 32)]
</code>
This screen dump of the object is quite useful to me.
<code>
>>> r = reversed(l)
>>> r
<listreverseiterator object at 0x009D2B90>
</code>
This screen dump of the object is less useful to me.
>From a pure programming point of view it's not a sufficient reason to
keep list comprehensions, especially as the interpreter shell could be
massaged into giving more output, but right here right now it's a lot
easier to read the former than the latter IMHO.
(That is assuming I'm right in assuming functions like "reversed" are
generator expressions).
Mark
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Robert Kern
No, generator expressions are like list comprehensions, only they create
generator objects.
(x*x for x in xrange(1000))
versus
[x*x for x in xrange(1000))
Of course, one can always get an explicit list by passing the generator
object to list(). This also works for most iterables like the one you
showed above.
list(x*x for x in xrange(1000))
--
Robert Kern
rk...@ucsd.edu
"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
-- Richard Harter