py: Fix errors are suppressed in generator comprehensions

Sequence.Iterate does not handle exceptions.
Iterate() should return error except StopIteration.

Author: corona10

py/sequence.go

@@ -93,10 +93,13 @@ func Iterate(obj Object, fn func(Object) bool) error {
 			return err
 		}
 		for {
-			item, finished := Next(iterator)
-			if finished != nil {
+			item, err := Next(iterator)
+			if err != nil && err == StopIteration {
 				break
 			}
+			if err != nil && err != StopIteration {
+				return err
+			}
 			if fn(item) {
 				break
 			}