[Python-ideas] Integrate some itertools into the Python syntax

[Ethan Furman]

On 03/22/2016 12:26 PM, Michel Desmoulin wrote:
> Le 22/03/2016 20:23, Ethan Furman a écrit :
>> On 03/22/2016 12:10 PM, Koos Zevenhoven wrote:
>>> On Tue, Mar 22, 2016 at 8:41 PM, Ethan Furman wrote:
>>>> On 03/22/2016 10:51 AM, Michel Desmoulin wrote:
>>>>
>>>>> def foo(p):
>>>>>        with open(p) as f:
>>>>>            def begin:
>>>>>                return x == "BEGIN SECTION"
>>>>>             def end:
>>>>>                return x == "STOP"
>>>>>            return f[begin, end][:10000]
>>>>>
>>>>> It's very clean, very convenient, very natural, and memory efficient.
>>>>
>>>>
>>>> Except the 10,000 limit doesn't happen until /after/ the end block is
>>>> reached -- which could be a million lines later.
>>>
>>>
>>> if f[begin, end] is a generator, the 10000 limit may happen before the
>>> end block is reached, which I think was the point.
>>
>> That is wrong, which was my point: the `[:10000]` doesn't take effect
>> until after `f[begin:end]` (whatever it is) is evaluated.
 >
> [begin, end] and [:10000] are applied one next() at a time.
>
> begin, then end, then :10000 for the first next(),
>
> then again in that order for the following next() call, etc.
>
> That's the whole point.

That may be the point, but that is not what the above code does.  Since 
you don't believe me, let's break it down:

f[begin:end] -> grabs a section of p.  This could be 5 lines or 50000000

[:10000] -> take the first 10000 of the previous result

return -> send those (up to) 10000 lines back

--
~Ethan~