lib.util.Namespace raises the expected exception

package/CHANGELOG

@@ -91,6 +91,8 @@ Fixes
   * Fixed selections using operators backwards ('prop 10 > mass') and sensitivity
     about whitespace around these (PR #1156 Issue #1011 #1009)
   * Fixed PSA analysis is now using AlignTraj
+  * The namespace used for auxiliary data now raises an AttributeError instead
+    of a KeyError when accessing data by attributes (Issue #1166)
 
 Changes
   * Started unifying the API of analysis classes (named internally

package/MDAnalysis/lib/util.py

@@ -1335,25 +1335,44 @@ class Namespace(object):
     """Class to allow storing attributes in new namespace. """
     def __getattr__(self, key):
         # a.this causes a __getattr__ call for key = 'this'
-        return self.__dict__[key]
+        try:
+            return self.__dict__[key]
+        except KeyError:
+            raise AttributeError('"{}" is not known in the namespace.'
+                                 .format(key))
+
     def __setattr__(self, key, value):
         # a.this = 10 causes a __setattr__ call for key='this' value=10
-        self.__dict__[key] = value
+        try:
+            self.__dict__[key] = value
+        except KeyError:
+            raise AttributeError('"{}" is not known in the namespace.'
+                                 .format(key))
+
     def __delattr__(self, key):
-        del self.__dict__[key]
+        try:
+            del self.__dict__[key]
+        except KeyError:
+            raise AttributeError('"{}" is not known in the namespace.'
+                                 .format(key))
+
     def __eq__(self, other):
         try:
             # this'll allow us to compare if we're storing arrays
             assert_equal(self.__dict__, other.__dict__)
         except AssertionError:
             return False
         return True
+
     def __str__(self):
         return str(self.__dict__)
+
     def __len__(self):
         return len(self.__dict__)
+
     def __getitem__(self, key):
         return self.__dict__[key]
+
     def __iter__(self):
         for i in self.__dict__:
             yield i

testsuite/MDAnalysisTests/coordinates/base.py

@@ -293,7 +293,7 @@ def test_add_same_auxname_raises_ValueError(self):
     def test_remove_auxiliary(self):
         self.reader.remove_auxiliary('lowf')
         assert_raises(AttributeError, getattr, self.reader._auxs, 'lowf')
-        assert_raises(KeyError, getattr, self.reader.ts.aux, 'lowf')
+        assert_raises(AttributeError, getattr, self.reader.ts.aux, 'lowf')
 
     @raises(ValueError)
     def test_remove_nonexistant_auxiliary_raises_ValueError(self):
@@ -344,7 +344,7 @@ def test_rename_aux(self):
         assert_equal(self.reader.ts.aux.lowf_renamed,
                      self.ref.aux_lowf_data[0])
         # old name should be removed
-        assert_raises(KeyError, getattr, self.reader.ts.aux, 'lowf')
+        assert_raises(AttributeError, getattr, self.reader.ts.aux, 'lowf')
         # new name should be retained
         next(self.reader)
         assert_equal(self.reader.ts.aux.lowf_renamed,