Replaced two lines repeated twice in function genmatrix with a function call, which is intended to be identical in effect, but provides an informative log message.

With this commit, the behaviour of the test_hierarchical.py test set remains identical to python-cluster 1.4.1 under both Python2.7 (which passes)_and Python3.5 (which fails with a KeyError thrown).

Author: tim-littlefair

cluster/matrix.py

@@ -22,6 +22,30 @@
 
 logger = logging.getLogger(__name__)
 
+def _encapsulate_item_for_combinfunc(item):
+    """
+    This function has been extracted in order to 
+    make Github issue #28 easier to investigate.
+    It replaces the following two lines of code, 
+    which occur twice in method genmatrix, just
+    before the invocation of combinfunc.
+        if not hasattr(item, '__iter__') or isinstance(item, tuple):
+            item = [item]
+    Logging has been added to the original two lines
+    and shows that the behaviour of this snippet
+    has changed between Python2.7 and Python3.5.
+    """
+    encapsulated_item = None
+    if not hasattr(item, '__iter__') or isinstance(item, tuple):
+        encapsulated_item = [item]
+    else:
+        encapsulated_item = item
+    logging.debug(
+        "item class:%s encapsulated as:%s ",
+        item.__class__, encapsulated_item.__class__
+    )
+    return encapsulated_item
+
 
 class Matrix(object):
     """
@@ -123,10 +147,17 @@ def genmatrix(self, num_processes=1):
                         num_tasks_completed += 1
                 else:
                     # Otherwise do it here, in line
+                    """
                     if not hasattr(item, '__iter__') or isinstance(item, tuple):
                         item = [item]
                     if not hasattr(item2, '__iter__') or isinstance(item2, tuple):
                         item2 = [item2]
+                    """
+                    # See the comment in function _encapsulate_item_for_combinfunc
+                    # for details of why the lines above have been replaced
+                    # by function invocations
+                    item = _encapsulate_item_for_combinfunc(item)
+                    item2 = _encapsulate_item_for_combinfunc(item2)
                     row[col_index] = self.combinfunc(item, item2)
 
             if self.symmetric: