Drop Python 2.6 support

[jml]

I propose that:

• the next release be the last release that supports Python 2.6
• we replace testtools.compat with a dependency on six

[thomir]

Can we get usage state from pypi regarding what versions people are downloading testtools for?

[rbtcollins]

I think these are independent things. To whit: six supports 2.6. For the use of six, I'm +1 straight up. 2.6 is more gnarly to reason about. When I dropped support for 2.6 from mock, the internets rebelled. OTOH see the setuptools dropping of 2.6....

[jml]

Fair call. Filed new ticket.

[hugovk]

Can we get usage state from pypi regarding what versions people are downloading testtools for?

Two years on, here's pip installs for testtools from PyPI from the last month:

$ pypinfo --percent --pip testtools pyversion
python_version percent download_count
-------------- ------- --------------
2.7              92.5%        186,663
3.5               4.8%          9,694
3.6               1.3%          2,723
3.4               1.1%          2,166
2.6               0.2%            444
3.3               0.1%            169
3.7               0.0%             16
None              0.0%              2

[freeekanayaka]

Let's kill 2.6, it's also EOL now.

It's pretty upsetting to see those numbers for 3.x. Does it means nobody is using testtools for new projects? Or are 2.7 projects using testtools still so massively used that the dilute the figures?

[hugovk]

2.6 has already been removed in #198, but see #265 for some more cleanup.

Hard to be sure about the Python 3.x numbers, but generally I've seen a higher share for other projects.

Here's for all projects:

⌂64% [hugo:/private/tmp/testtools] rm-2.6(+2/-11) 127 ± pypinfo --percent --pip "" pyversion
python_version percent download_count
-------------- ------- --------------
2.7              77.7%    496,057,092
3.6               8.7%     55,664,224
3.5               7.7%     49,128,413
3.4               4.4%     27,773,357
2.6               1.3%      8,279,744
3.3               0.1%        757,054
3.7               0.1%        368,748
3.2               0.0%         50,871
None              0.0%         22,005
2.8               0.0%            188
3.1               0.0%            125

More stats for this one:

[hugo:/private/tmp/testtools] rm-2.6(+2/-11) 2s 2 ± pypinfo --percent --pip testtools system percent2 percent3
system_name       percent_2 percent_3 percent download_count
----------------- --------- --------- ------- --------------
Linux             93.0      7.0         99.2%        203,533
Windows           53.1      46.9         0.4%            907
Darwin            80.4      19.6         0.4%            779
FreeBSD           86.7      13.3         0.0%             15
CYGWIN_NT-6.1     50.0      50.0         0.0%              2
CYGWIN_NT-6.1-WOW 0.0       100.0        0.0%              1
CYGWIN_NT-6.3-WOW 100.0     0.0          0.0%              1
MSYS_NT-6.1       100.0     0.0          0.0%              1
CYGWIN_NT-10.0    0.0       100.0        0.0%              1
Java              0.0       0.0          0.0%              1

⌂61% [hugo:/private/tmp/testtools] rm-2.6(+2/-11) 5s ± pypinfo --pip testtools distro percent2 percent3
distro_name                     percent_2 percent_3 download_count
------------------------------- --------- --------- --------------
Ubuntu                          92.9      7.1              141,797
CentOS Linux                    97.4      2.6               25,902
None                            94.2      5.8                9,961
Virtuozzo                       100.0     0.0                8,473
Debian GNU/Linux                72.8      27.2               5,452
Red Hat Enterprise Linux Server 98.4      1.6                2,972
Fedora                          98.0      2.0                2,830
Alpine Linux                    38.0      62.0               1,870
CentOS                          90.6      9.4                1,486
debian                          95.3      4.7                1,032
macOS                           79.6      20.4                 712
openSUSE Leap                   92.1      7.9                  381
RedHatEnterpriseServer          97.4      2.6                  341
Linux Mint                      81.2      18.8                 335
DaterOS Linux                   100.0     0.0                  282
SLES                            100.0     0.0                  261
Astra Linux (Smolensk)          0.0       100.0                241
Red Hat Enterprise Linux Client 100.0     0.0                  184
Oracle Linux Server             99.0      1.0                  103
Arch Linux                      54.9      45.1                  82

[hugo:/private/tmp/testtools] rm-2.6(+2/-11) 7s ± pypinfo --pip testtools distro distro-version percent2 percent3
distro_name                     distro_version percent_2 percent_3 download_count
------------------------------- -------------- --------- --------- --------------
Ubuntu                                   16.04 93.0      7.0              102,150
Ubuntu                                   14.04 92.1      7.9               33,619
CentOS Linux                                 7 97.8      2.2               25,121
None                                      None 94.2      5.8                9,961
Virtuozzo                                    7 100.0     0.0                8,473
Debian GNU/Linux                             8 69.0      31.0               4,220
Ubuntu                                   16.10 99.1      0.9                3,390
Ubuntu                                   17.04 89.6      10.4               1,735
Red Hat Enterprise Linux Server            7.4 97.4      2.6                1,223
Red Hat Enterprise Linux Server            7.3 98.9      1.1                1,219
Fedora                                      22 99.9      0.1                  902
debian                              jessie/sid 95.7      4.3                  861
Alpine Linux                             3.6.2 52.3      47.7                 831
Fedora                                      24 100.0     0.0                  823
Ubuntu                                   12.04 98.1      1.9                  788
Debian GNU/Linux                             9 85.9      14.1                 702
Alpine Linux                             3.4.6 27.2      72.8                 610
CentOS                                     6.8 99.8      0.2                  484
Fedora                                      26 93.9      6.1                  479
CentOS                                     6.9 98.3      1.7                  467