fix exceptions in File.__getitem__() (h/t @kmulvaney) (#22)

* fix exceptions in File.__getitem__() (h/t @kmulvaney)

- commit 310c751 introduced Python 3-specific syntax (raise … from …)
  that broke Python 2. Replace with a method from python-future.

* move raise_from import to pycompat submodule

* fix undeclared encoding in test_gdx.py

* remove an unnecessary Unicode character in File.info()

* complete previous

gdx/__init__.py

@@ -11,7 +11,7 @@
 import pandas
 import xarray as xr
 
-from .pycompat import install_aliases, filter, range, super, zip
+from .pycompat import install_aliases, filter, raise_from, range, super, zip
 install_aliases()
 
 from .api import GDX, gdxcc, type_str, vartype_str
@@ -408,7 +408,7 @@ def info(self, name):
         """Informal string representation of the Symbol with *name*."""
         if isinstance(self._state[name], dict):
             attrs = self._state[name]['attrs']
-            return '{} {}({}) — {} records: {}'.format(
+            return '{} {}({}), {} records: {}'.format(
                 attrs['type_str'], name, ','.join(attrs['domain']),
                 attrs['records'], attrs['description'])
         else:
@@ -474,4 +474,4 @@ def __getitem__(self, key):
                 self._load_symbol_data(key)
                 return super(File, self).__getitem__(key)
             else:
-                raise KeyError(key) from e
+                raise raise_from(KeyError(key), e)

gdx/pycompat.py

@@ -2,6 +2,7 @@
 
 from builtins import filter, range, object, super, zip
 from future.standard_library import install_aliases
+from future.utils import raise_from
 
 PY3 = sys.version_info[0] >= 3
 

gdx/test/test_gdx.py

@@ -133,7 +133,7 @@ def test_info1(self, gdxfile):
 
     def test_info2(self, rawgdx):
         # Use a File where p1 is guaranteed to not have been loaded:
-        assert (gdx.File(rawgdx).info('p1') == 'unknown parameter p1(s) — 1 '
+        assert (gdx.File(rawgdx).info('p1') == 'unknown parameter p1(s), 1 '
                 'records: Example parameter with animal data')
 
     def test_dealias(self, gdxfile):