[Python-ideas] + operator on generators

[Koos Zevenhoven]

On Mon, Jun 26, 2017 at 4:53 PM, Serhiy Storchaka <storchaka at gmail.com>
wrote:

> 26.06.17 13:47, Joao S. O. Bueno пише:
>
>> On 25 June 2017 at 20:55, Danilo J. S. Bellini <danilo.bellini at gmail.com
>> <mailto:danilo.bellini at gmail.com>> wrote:
>>
>>     On Sun, Jun 25, 2017 at 3:06 PM, lucas via Python-ideas
>>     <python-ideas at python.org
>>     <mailto:python-ideas at python.org>>wrote:
>>
>>         I often use generators, and itertools.chain on them.
>>         What about providing something like the following:
>>
>>              a = (n for n in range(2))
>>              b = (n for n in range(2, 4))
>>              tuple(a + b)  # -> 0 1 2 3
>>
>>
>> You know you can do `tuple(*a, *b)` , right?
>>
>> The problem with the "*" notation is that it will actually render the
>> iterable
>> contents eagerly - unlike something that would just chain them.
>> But for creating tuples, it just works.
>>
>
> Even the tuple constructor is not needed.
>
> >>> *a, *b
> (0, 1, 2, 3)
>

​And you can also do

def a_and_b():
    yield from a
    yield from b

c = a_and_b() # iterable that yields 0, 1, 2, 3


I sometimes wish there was something like

c from:
    yield from a
    yield from b

​...or to get a list:

c as list from:
    yield from a
    yield from b

...or a sum:

c as sum from:
    yield from a
    yield from b

These would be great for avoiding crazy oneliner generator expressions.
They would also be equivalent to things like:

@list
@from
def c():
    yield from a
    yield from b

@sum
@from
def c():
    yield from a
    yield from b

the above, given:
    def from(genfunc):
        return genfunc()

Except of course `from` is a keyword and it should probably just be `call`.
​
But this still doesn't naturally extend to allow indexing and slicing, like
c[2] and c[1:3], for the case where the concatenated iterables are
Sequences.

-- Koos


-- 
+ Koos Zevenhoven + http://twitter.com/k7hoven +
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