added extras execute_batch for executemany

[vir-mir]

I added this function, since it allows you to quickly insert values ​​into the database.

This solves the executemany problem, more details can be found in this issues psycopg/psycopg2#491

I wrote several of my performance tests that showed the following result.
insert 10000 query in database

test first https://github.com/vir-mir/kdr2019/tree/master/test2
aiopg not execute_batch: 18.12 sec
asyncpg: 10.09 sec

test second https://github.com/vir-mir/kdr2019/tree/master/test3
aiopg execute_batch: 0.64 sec
asyncpg: 10.09 sec

[codecov]

Codecov Report

Merging #632 into master will increase coverage by 0.03%.
The diff coverage is 94.44%.

@@            Coverage Diff             @@
##           master     #632      +/-   ##
==========================================
+ Coverage   92.18%   92.22%   +0.03%     
==========================================
  Files          10       11       +1     
  Lines        1037     1055      +18     
  Branches      121      126       +5     
==========================================
+ Hits          956      973      +17     
  Misses         65       65              
- Partials       16       17       +1

Impacted Files	Coverage Δ
aiopg/extras.py	94.44% <94.44%> (ø)

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[lgtm-com]

This pull request introduces 1 alert when merging ccd5a46 into 2911c10 - view on LGTM.com

new alerts:

• 1 for Unguarded next in generator

[iAnanich]

When this could be merged? Can't wait to use it )

[andrey-berenda]

import itertools 


def _paginate(seq, page_size):
    it = iter(seq)
    page = list(itertools.islice(it, 0, page_size))
    while page:
        yield page
        page = list(itertools.islice(it, 0, page_size))

I think it is better solution

[andrey-berenda]

with this solution you can use iterators in _paginate
for example
_paginate(range(1, 8), 3)

[andrey-berenda]

@pytest.mark.parametrize(
    'data, expected_pages',
    (
            (
                    (1, 2, 3, 4, 5, 6, 7), [
                        [1, 2, 3],
                        [4, 5, 6],
                        [7],
                    ]
            ),
            (
                    (1, 2, 3, 4, 5, 6), [
                        [1, 2, 3],
                        [4, 5, 6],
                    ]
            ),
    )
)
def test__paginate(data, expected_pages):
    for page, expected_page in itertools.zip_longest(
            _paginate(data, page_size=3),
            expected_pages,
    ):
        assert page == expected_page

[vir-mir]

thanks!