On 11/22/2014 07:06 PM, Chris Angelico wrote:
On Sun, Nov 23, 2014 at 11:51 AM, Ron Adam<ron3...@gmail.com> wrote:
>
>
>On 11/22/2014 06:20 PM, Chris Angelico wrote:
>>
>>Hmmm, there's no such thing as tuple comprehensions.
>
>Just didn't think it through quite well enough. But you are correct, that
>would be a generator expression.
>
>One less case to worry about.:-)
Ah right, no probs.
>>> >And it would be changed to this...
>>> >
>>> > def comp_expression():
>>> > for x in itr: # StopIteration caught here.
>>> > if cond:
>>> > list.append(expr)
>>> >
>>> > # StopIteration from cond and expr caught here.
>>> > lst = list(x for x in comp_expression())
>
>Right, the list.append() should be a yield(expr).
In that case, your second generator expression is entirely redundant;
all you want is list(comp_expression()).
Yes, and that is good. Simplies it even more.
But the example doesn't say
*why* this version should terminate on a StopIteration raised by expr,
when the statement form would print an exception traceback.
I presume you are asking why do this? And not why the example does that?
There has been a desires expressed, more than a few times, to make
comprehensions more like generator expressions in the past. It looks to me
that that desire is still true. I also think there has been quite a bit of
confusion in these discussions that could be reduced substantially by
making Comprehensions work a bit more like generator expressions.
As to why the example does that.. a list constructor iterates over a
generator expression in a way that follows the iterator protocol. If you
make comprehsionsons work as if they are a generator expression fed to a
constructor... then it too should follow the itorator protocol. Do you agree?
>The real question is how much breakage would such a change make? That will
>probably need a patch in order to test it out.
There's one attached here:
http://bugs.python.org/issue22906
Doesn't that patch effect generators and not comprehensions? If so, it
wouldn't do what we are talking about here.
Ron
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