Merge pull request #937 from mathics/Python2-divide-incompatibility

Fix runtime bugs seen from GS3.m in per_expr()

Author: rocky

mathics/core/pattern.py

@@ -322,17 +322,21 @@ def per_expr(yield_expr, expr_groups, sum=0):
 
                         if expr_groups:
                             expr, count = expr_groups.popitem()
-                            max_per_pattern = count / len(patterns)
+                            max_per_pattern = count // len(patterns)
                             for per_pattern in range(max_per_pattern, -1, -1):
                                 for next in per_expr(   # nopep8
                                     expr_groups, sum + per_pattern):
                                     yield_expr([expr] * per_pattern + next)
                         else:
                             if sum >= match_count[0]:
                                 yield_expr([])
+                            # Until we learn that the below is incorrect, we'll return basically no match.
+                            yield None
 
                     # for sequence in per_expr(expr_groups.items()):
                     def yield_expr(sequence):
+                        # FIXME: this call is wrong and needs a
+                        # wrapper_function as the 1st parameter.
                         wrappings = self.get_wrappings(
                             sequence, match_count[1], expression, attributes)
                         for wrapping in wrappings: