Drop support for Python 2.7!

[zbruick]

Description Of Changes

What do you do when it's a Friday afternoon? Drop 2.7!

In all seriousness, according to our docs, we're dropping 2.7 in "Fall 2019". Given that meteorological (real) fall is here and astronomical fall is 8 days away, this is likely for sure going in 0.12. (Not sure when 0.11 will get out the door, but not sure if we should include this in that or not).

I'm sure I missed some stuff, so feel free to push commits to this, or review and comment if you have small items to address. There is one open item on #801 that I didn't fix yet, as the comment was vague and I didn't have time to look into it yet.

Whenever 2.7 is dropped, celebration is in order!

Checklist

• Closes Dropping support for Python 2.7 #801
• Fully documented

[dopplershift]

One good one to do to modernize the code base is to convert all uses of super to just super().

[dopplershift]

Actually, before doing that, it might be good to see what we can do about having flake8 catch that, and other modernizations, that we make.

[dopplershift]

Another one to add is updating setup.cfg to remove dependencies (I'm sure you had before I rewrote the build system) as well as remove the bdist_wheel section to no longer say we build universal wheels.

[dopplershift]

Other things coming to mind:

• In several places we have code that does some hacking around the crappy function signature support on Python 2.7. We can clean that up.
• A lot of places using kwargs.pop should probably be changed to use kw-only arguments

[zbruick]

Actually, before doing that, it might be good to see what we can do about having flake8 catch that, and other modernizations, that we make.

Have been looking for any plugins and haven't seen anything useful yet. Lots of py2 to py 2/3 support online. Doesn't really look like there are any good linters for conversion of py2/3 to py3. Looking at astropy, they suggested running coverage just with py2 and py3 separately to see what was only covered in either to remove dead code. Is that something that can easily be done here?

[zbruick]

Ok I've cleaned up setup.cfg and removed uses of kwargs.pop wherever possible (only remaining ones are within the plot module).

[zbruick]

• In several places we have code that does some hacking around the crappy function signature support on Python 2.7. We can clean that up.

Clarification on where these hacks exist (or what they look like) would be great

[dopplershift]

I’ll look at the signature stuff. We should be able to look at codecov and see what it says about new uncovered lines with this PR to find other blocks of unneeded code (assuming it’s working).

[zbruick]

Found one thing in units.py that could be removed. I believe the only things that were mentioned that haven't been done is to update super() and clean up hacks.

[lgtm-com]

This pull request fixes 1 alert when merging c12386a into 7e506b8 - view on LGTM.com

fixed alerts:

• 1 for Inconsistent equality and hashing

[zbruick]

Fixed imports in grid.py and tools.py.

Added errors to setup.py and init.py if Python 2 is detected to either fail to install or fail to import. Verified that the error message in setup.py is returned in pip install -e. is executed in a Py2 environment.

[lgtm-com]

This pull request fixes 1 alert when merging 5fe6f23 into d39ddc3 - view on LGTM.com

fixed alerts:

• 1 for Inconsistent equality and hashing

[lgtm-com]

This pull request fixes 1 alert when merging ae563df into d39ddc3 - view on LGTM.com

fixed alerts:

• 1 for Inconsistent equality and hashing

[dopplershift]

Power-cycling to hopefully get codecov to actually track results--really want to see if there are any newly uncovered lines after this.

[lgtm-com]

This pull request fixes 1 alert when merging 602d30f into d39ddc3 - view on LGTM.com

fixed alerts:

• 1 for Inconsistent equality and hashing

[lgtm-com]

This pull request fixes 1 alert when merging 4ccb2c9 into d39ddc3 - view on LGTM.com

fixed alerts:

• 1 for Inconsistent equality and hashing