Consolidate some code and speed up StepParentMixin

mentoring/components/step.py

@@ -17,6 +17,7 @@
 # along with this program in a file in the toplevel directory called
 # "AGPLv3".  If not, see <http://www.gnu.org/licenses/>.
 #
+from .utils import child_isinstance
 
 
 class StepParentMixin(object):
@@ -27,15 +28,9 @@ class StepParentMixin(object):
     @property
     def steps(self):
         """
-        Generator returning the usage_id for all of this XBlock's
-        children that are "Steps"
+        Get the usage_ids of all of this XBlock's children that are "Steps"
         """
-        step_ids = []
-        for child_id in self.children:
-            child = self.runtime.get_block(child_id)
-            if isinstance(child, StepMixin):
-                step_ids.append(child_id)
-        return step_ids
+        return [child_id for child_id in self.children if child_isinstance(self, child_id, StepMixin)]
 
 
 class StepMixin(object):

mentoring/components/table.py

@@ -25,6 +25,8 @@
 
 import errno
 
+from .utils import child_isinstance
+
 from xblock.core import XBlock
 from xblock.fields import Scope, String
 from xblock.fragment import Fragment
@@ -120,7 +122,7 @@ class MentoringTableColumnBlock(XBlock):
         """
         return self._render_table_view(
             view_name='mentoring_table_view',
-            id_filter=lambda child_id: not issubclass(self._get_child_class(child_id), MentoringTableColumnHeaderBlock),
+            id_filter=lambda child_id: not child_isinstance(self, child_id, MentoringTableColumnHeaderBlock),
             template='mentoring-table-column.html',
             context=context
         )
@@ -131,20 +133,11 @@ class MentoringTableColumnBlock(XBlock):
         """
         return self._render_table_view(
             view_name='mentoring_table_header_view',
-            id_filter=lambda child_id: issubclass(self._get_child_class(child_id), MentoringTableColumnHeaderBlock),
+            id_filter=lambda child_id: child_isinstance(self, child_id, MentoringTableColumnHeaderBlock),
             template='mentoring-table-header.html',
             context=context
         )
 
-    def _get_child_class(self, child_id):
-        """
-        Helper method to get a block type from a usage_id without loading the block.
-
-        Returns the XBlock subclass of the child block.
-        """
-        type_name = self.runtime.id_reader.get_block_type(self.runtime.id_reader.get_definition_id(child_id))
-        return self.runtime.load_block_type(type_name)
-
 
 class MentoringTableColumnHeaderBlock(XBlock):
     """

mentoring/components/utils.py

+"""
+Helper methods
+
+Should eventually be moved to xblock-utils.
+"""
+
+
+def child_isinstance(block, child_id, block_class_or_mixin):
+    """
+    Is "block"'s child identified by usage_id "child_id" an instance of
+    "block_class_or_mixin"?
+
+    This is a bit complicated since it avoids the need to actually
+    instantiate the child block.
+    """
+    def_id = block.runtime.id_reader.get_definition_id(child_id)
+    type_name = block.runtime.id_reader.get_block_type(def_id)
+    child_class = block.runtime.load_block_type(type_name)
+    return issubclass(child_class, block_class_or_mixin)

mentoring/tests/unit/test_step.py

@@ -12,7 +12,11 @@ class Parent(StepParentMixin):
 
     @property
     def runtime(self):
-        return Mock(get_block=lambda i: self._children[i])
+        return Mock(
+            get_block=lambda i: self._children[i],
+            load_block_type=lambda i: type(self._children[i]),
+            id_reader=Mock(get_definition_id=lambda i: i, get_block_type=lambda i: i)
+        )
 
     def _set_children_for_test(self, *children):
         self._children = children
@@ -24,7 +28,11 @@ class Parent(StepParentMixin):
                 pass
 
 
-class Step(StepMixin):
+class BaseClass(object):
+    pass
+
+
+class Step(BaseClass, StepMixin):
     def __init__(self):
         pass