Drop support for EOL Python

[hugovk]

Fixes #46.

EOL Python versions are no longer supported by the core Python team and no longer receive security updates.

https://en.wikipedia.org/wiki/CPython#Version_history

They're also little used. Here's the pip installs for Blinker from PyPI for last month:

python_version	percent	download_count
2.7	50.71%	88,260
3.6	28.01%	48,749
3.5	14.50%	25,235
3.4	6.41%	11,153
3.3	0.17%	290
3.7	0.13%	234
2.6	0.08%	131
3.2	0.00%	2

Source: pypinfo --start-date -49 --end-date -22 --percent --pip --markdown Blinker pyversion

Dropping them eases the maintenance burden and allows more modern features of Python to be used, some of which is included here.

[hugovk]

Updated to add python_requires to help pip, and upgrade Python syntax using https://github.com/asottile/pyupgrade.

Here's pip installs for June 2018:

python_version	percent	download_count
3.6	42.43%	69,300
2.7	38.80%	63,378
3.5	14.65%	23,924
3.4	3.72%	6,082
3.7	0.29%	468
3.3	0.05%	85
2.6	0.05%	74
3.2	0.01%	22
None	0.00%	2
3.8	0.00%	1
Total		163,336

Source: pypinfo --start-date 2018-06-01 --end-date 2018-06-30 --percent --markdown Blinker pyversion

[ThomasWaldmann]

looks good. just the jython/pypy versions need checking.

some stuff might be matter of taste (e.g. dict literals vs. using dict(x=...) or % vs. .format()).

[hugovk]

Checking in: is there anything more I can do for this? Thank you!

[RDIL]

2.7 dies in a little more then a month, I think that also needs removing.

[ThomasWaldmann]

@RDIL no, I don't think 2.7 should be removed in the near future.

There might be still applications in python 2.7 which did not port / finish porting to py3 yet.

Thus, while old py3 versions can be dropped quickly, we should support py27 for a longer while still due to that.

[hugovk]

This PR is only for Python 2.4 - 2.6 and 3.0 - 3.4, all of which have low to zero download numbers.

October 2019:

category	percent	downloads
3.6	37.69%	408,481
3.7	29.76%	322,536
2.7	23.68%	256,637
3.5	4.95%	53,644
3.4	1.86%	20,187
3.8	1.38%	14,949
null	0.68%	7,402
2.6	0.00%	53
3.9	0.00%	4
3.2	0.00%	1
3.3	0.00%	1
Total		1,083,895

Source: pip install -U pypistats && pypistats python_minor blinker --last-month

[RDIL]

Thats fair

[jek]

Thanks for this. I don't have any conceptual issue with supporting older Python versions, though at some point the test infrastructure becomes difficult to maintain & it feels ok to shed a bit of this burden.

I don't have any intention of dropping 2.7 support for some time.

Python 3.8 positional-only parameters finally bring a portable way of fixing the (*args, **kwargs) hack on the send() method. If I were still actively working in Python (sadly I am not), I would look at making 3.8 the preferred native source version for Blinker and move all prior versions (2.7 and <3.8) to compatibility fallbacks.