remove python 2 lines (#757)

* Resolve merge conflicts.

The upstream what's new file had been updated.

* Remove py2 and Windows checks.

Removed because python 2 is no longer supported, and this let us remove the
checks for Windows too.

* Remove from __future__ import print_function.

* Remove from __future__ import division.

* Revert "Remove py2 and Windows checks."

This reverts commit a762fc3.

* Remove has_python2 checks.

* Remove duplicate line in what's new file.

* Remove python2-sensitive imports.

* Remove out-of-date python2 comment.

* Import JSONDecodeError directly in py3 way.

* Change Tkinter import (py2) to tkinter (py3).

* Update import configparser to only py3 version.

* Update documentation comment.

* Remove strict arguments.

The case where these were relevant (Windows build using Python 2) is no
longer used because Python 2 is no longer supported.

* Remove platform_is_windows import.

It is no longer used.

* Set strict arg to True for two tests.

* Fix indentation mistake.

Convert tabs to spaces.

* Revert "Remove from __future__ import print_function."

This reverts commit 0508b33.
This also undoes the changes to how configparser is imported.

Author: alexandermorgan

pvlib/atmosphere.py

@@ -3,8 +3,6 @@
 absolute airmass and to determine pressure from altitude or vice versa.
 """
 
-from __future__ import division
-
 from warnings import warn
 
 import numpy as np
@@ -211,8 +209,7 @@ def get_relative_airmass(zenith, model='kastenyoung1989'):
     Sandia Report, (2012).
     '''
 
-    # need to filter first because python 2.7 does not support raising a
-    # negative number to a negative power.
+    # set zenith values greater than 90 to nans
     z = np.where(zenith > 90, np.nan, zenith)
     zenith_rad = np.radians(z)
 

pvlib/clearsky.py

@@ -3,8 +3,6 @@
 to calculate clear sky GHI, DNI, and DHI.
 """
 
-from __future__ import division
-
 import os
 from collections import OrderedDict
 import calendar

pvlib/iotools/ecmwf_macc.py

@@ -2,7 +2,6 @@
 Read data from ECMWF MACC Reanalysis.
 """
 
-from __future__ import division
 import threading
 import pandas as pd
 

pvlib/iotools/epw.py

@@ -3,13 +3,7 @@
 """
 
 import io
-
-try:
-    # python 2 compatibility
-    from urllib2 import urlopen, Request
-except ImportError:
-    from urllib.request import urlopen, Request
-
+from urllib.request import urlopen, Request
 import pandas as pd
 
 

pvlib/iotools/psm3.py

@@ -7,11 +7,7 @@
 import io
 import requests
 import pandas as pd
-# Python-2 compatible JSONDecodeError
-try:
-    from json import JSONDecodeError
-except ImportError:
-    JSONDecodeError = ValueError
+from json import JSONDecodeError
 
 URL = "http://developer.nrel.gov/api/solar/nsrdb_psm3_download.csv"
 

pvlib/iotools/surfrad.py

@@ -2,13 +2,7 @@
 Import functions for NOAA SURFRAD Data.
 """
 import io
-
-try:
-    # python 2 compatibility
-    from urllib2 import urlopen, Request
-except ImportError:
-    from urllib.request import urlopen, Request
-
+from urllib.request import urlopen, Request
 import pandas as pd
 import numpy as np
 

pvlib/iotools/tmy.py

@@ -5,13 +5,7 @@
 import datetime
 import io
 import re
-
-try:
-    # python 2 compatibility
-    from urllib2 import urlopen, Request
-except ImportError:
-    from urllib.request import urlopen, Request
-
+from urllib.request import urlopen, Request
 import dateutil
 import pandas as pd
 
@@ -160,7 +154,7 @@ def read_tmy3(filename=None, coerce_year=None, recolumn=True):
         try:
             filename = _interactive_load()
         except ImportError:
-            raise ImportError('Interactive load failed. Tkinter not supported '
+            raise ImportError('Interactive load failed. tkinter not supported '
                               'on this system. Try installing X-Quartz and '
                               'reloading')
 
@@ -210,9 +204,9 @@ def read_tmy3(filename=None, coerce_year=None, recolumn=True):
 
 
 def _interactive_load():
-    import Tkinter
-    from tkFileDialog import askopenfilename
-    Tkinter.Tk().withdraw()  # Start interactive file input
+    import tkinter
+    from tkinter.filedialog import askopenfilename
+    tkinter.Tk().withdraw()  # Start interactive file input
     return askopenfilename()
 
 
@@ -406,7 +400,7 @@ def read_tmy2(filename):
         try:
             filename = _interactive_load()
         except ImportError:
-            raise ImportError('Interactive load failed. Tkinter not supported '
+            raise ImportError('Interactive load failed. tkinter not supported '
                               'on this system. Try installing X-Quartz and '
                               'reloading')
 

pvlib/irradiance.py

@@ -4,8 +4,6 @@
 irradiance, and total irradiance under various conditions.
 """
 
-from __future__ import division
-
 import datetime
 from collections import OrderedDict
 from functools import partial

pvlib/pvsystem.py

@@ -3,16 +3,10 @@
 performance of PV modules and inverters.
 """
 
-from __future__ import division
-
 from collections import OrderedDict
 import io
 import os
-try:
-    from urllib2 import urlopen
-except ImportError:
-    from urllib.request import urlopen
-
+from urllib.request import urlopen
 import numpy as np
 import pandas as pd
 
@@ -1787,14 +1781,8 @@ def retrieve_sam(name=None, path=None):
         else:
             csvdata = path
     elif name is None and path is None:
-        try:
-            # python 2
-            import Tkinter as tkinter
-            from tkFileDialog import askopenfilename
-        except ImportError:
-            # python 3
-            import tkinter
-            from tkinter.filedialog import askopenfilename
+        import tkinter
+        from tkinter.filedialog import askopenfilename
 
         tkinter.Tk().withdraw()
         csvdata = askopenfilename()

pvlib/solarposition.py

@@ -8,7 +8,6 @@
 # Tony Lorenzo (@alorenzo175), University of Arizona, 2015
 # Cliff hansen (@cwhanse), Sandia National Laboratories, 2018
 
-from __future__ import division
 import os
 import datetime as dt
 try: