Add remaining Python 3 builtins via six

[QuLogic]

To follow up on #1699, this adds the compatibility builtins on all files. This will look bigger because it's based on #1699, but I want to be sure tests can pass here too.

Much like the __future__ imports, this PR adds six imports that change behaviour of builtin functions. This is a blanket change, so hopefully it's not too hard to go through again. At least this time there's a functional change involved.

[QuLogic]

New tests are being added that do not use this new behaviour; please merge soon.

[rhattersley]

Looks like there are some unwanted commits on this branch as it stands.

[QuLogic]

I did a merge instead of a rebase to show the changes to the new files, but I'm not sure why the new commits from master are now showing as part of the PR.

[QuLogic]

GitHub is being weird, it seems, because I see only three new commits locally:

$ git cherry master py3k-six-global-builtin 
+ d517878ab73b27dbe3ef2fbc578fc5b149bbf556
+ 6c02f5d011e0d73868f34f109943cb0f5d63d28c
+ 537e246484708b1a58cafcd65d87603553dca9c3

[QuLogic]

This is now flat again. BTW, you can check that it only changes what I say it changes like this:

$ git log -1 -p a552c3e | grep '^-' | grep -v '^---' | sort -u
-# (C) British Crown Copyright 2010 - 2014, Met Office
-# (C) British Crown Copyright 2012 - 2014, Met Office
-# (C) British Crown Copyright 2013 - 2014, Met Office
-# (C) British Crown Copyright 2014, Met Office
-copyright = u'British Crown Copyright 2010 - 2014, Met Office'
-from six.moves import filter
-from six.moves import filter, map, range
-from six.moves import filter, map, range, zip
-from six.moves import filter, range
-from six.moves import filter, range, zip
-from six.moves import filter, zip
-from six.moves import map
-from six.moves import map, range, zip
-from six.moves import map, zip
-from six.moves import range
-from six.moves import range, zip
-from six.moves import zip

$ git log -1 -p a552c3e | grep '^+' | grep -v '^+++' | sort -u
+# (C) British Crown Copyright 2010 - 2015, Met Office
+# (C) British Crown Copyright 2012 - 2015, Met Office
+# (C) British Crown Copyright 2013 - 2015, Met Office
+# (C) British Crown Copyright 2014 - 2015, Met Office
+copyright = u'British Crown Copyright 2010 - 2015, Met Office'
+from six.moves import (filter, input, map, range, zip)  # noqa

[pelson]

To follow up on #1699, this adds the compatibility builtins on all files

I thought we'd decided not to do this? I'm not that keen on the change, though wouldn't block it. Just to be completely clear, are all of these changes necessary, or are they done for consistency with all other source files?

[QuLogic]

No, I think you're thinking of #1675 which added six imports but had no real impact on anything. This PR, on the other hand, imports the builtins that were changed in Python 3. So, much like the __future__ imports, it ensures consistency across 2 and 3.

[rhattersley]

from six.moves import (filter, input, map, range, zip) # noqa

As a reminder to myself, the noqa tag stops flake8 from complaining about the unused imports.

[rhattersley]

👍 Top marks for persistence @QuLogic!

[QuLogic]

👍 Top marks for persistence @QuLogic!

That and some patience! 😉