Location Timezone support for python3 newstr

[lukewitmer]

Things have been quiet for a while. Hope the fall is going well for all of you so far!

The following code

from __future__ import (absolute_import, division,
                        print_function, unicode_literals)
from builtins import *
from pvlib.location import Location
tz = -10
str_tz = 'Etc/GMT+' + str(-1*int(tz))
my_loc = Location(20.0, -155.9, str_tz, 105.0, "my_place")

gives the following exception:

Traceback (most recent call last):
  File "/Users/lucas/Documents/Code/sim/pv.py", line 52, in <module>
    my_loc = Location(20.0, -155.9, str_tz, 105.0, "my_place")
  File "/usr/local/lib/python2.7/site-packages/pvlib/location.py", line 76, in __init__
    raise TypeError('Invalid tz specification')
TypeError: Invalid tz specification

The most straightforward fix is, in location.py, to check isinstance(tz, basestring) instead of str on line 66. This makes it compatible across python 2 and 3.

[lukewitmer]

The fix is just one word in location.py, but I can't make the change as I seemingly don't have permission to push my branch for a PR. I'm fine if someone else simply makes the fix, but if I can have permission to contribute to branches for PRs, that would be nice :) thanks!

git -c diff.mnemonicprefix=false -c core.quotepath=false -c credential.helper=sourcetree push -v --tags --set-upstream origin refs/heads/Issue244-location-compatibility:refs/heads/Issue244-location-compatibility 
Pushing to https://github.com/pvlib/pvlib-python.git
remote: Permission to pvlib/pvlib-python.git denied to lukewitmer.
fatal: unable to access 'https://github.com/pvlib/pvlib-python.git/': The requested URL returned error: 403
Completed with errors, see above

[wholmgren]

To maybe make things a little more clear for future readers, the problem is that in the example above, str_tz = 'Etc/GMT+' + str(-1*int(tz)) is not actually a pure str. Rather, the from __future__ import unicode_literals statement means that Python 2 will interpret that "string" as unicode (same behavior as the default in Python 3). In Python 2, this presents a problem for the Location class constructor since it's looking for str but getting unicode instead.

We'd welcome a fix for this. To make a PR, you need to fork the library, push the changes to your fork, and make the PR from your fork. Please also add a test to test_location.py, probably just by adding u'Etc/GMT+7' or similar to the test_location_tz parametrize list.

[lukewitmer]

Thanks Will. I wasn't familiar with the forking workflow. I think I have it now. PR is in and was running through some checks. Thanks!