first pass in capa cleanup:

   - responsetype used to be instantiated multiple times(!) in capa_problem
     now it is instantiated once, and stored in self.responders
   - responsetypes.GenericResponse restructured; each superclass
     show now provide setup_response (and not __init__), and may
     provide get_max_score(); general __init__ provided to
     clean up superclasses.

common/lib/capa/util.py

+from calc import evaluator, UndefinedVariable
+
+#-----------------------------------------------------------------------------
+#
+# Utility functions used in CAPA responsetypes
+
+def compare_with_tolerance(v1, v2, tol):
+    ''' Compare v1 to v2 with maximum tolerance tol
+    tol is relative if it ends in %; otherwise, it is absolute
+    '''
+    relative = "%" in tol
+    if relative: 
+        tolerance_rel = evaluator(dict(),dict(),tol[:-1]) * 0.01
+        tolerance = tolerance_rel * max(abs(v1), abs(v2))
+    else: 
+        tolerance = evaluator(dict(),dict(),tol)
+    return abs(v1-v2) <= tolerance
+
 def contextualize_text(text, context): # private
     ''' Takes a string with variables. E.g. $a+$b. 
     Does a substitution of those variables from the context '''

lms/djangoapps/courseware/module_render.py

@@ -169,7 +169,7 @@ def render_x_module(user, request, xml_module, module_object_preload, position=N
     content = instance.get_html()
 
     # special extra information about each problem, only for users who are staff 
-    if user.is_staff:
+    if False and user.is_staff:
         module_id = xml_module.get('id')
         histogram = grade_histogram(module_id)
         render_histogram = len(histogram) > 0

lms/static/coffee/src/modules/problem.coffee

@@ -48,7 +48,7 @@ class @Problem
               @$("label[for='input_#{key}_#{choice}']").attr
                 correct_answer: 'true'
           else
-            @$("#answer_#{key}").text(value)
+            @$("#answer_#{key}").html(value)	// needs to be html, not text, for complex solutions (eg coding)
         @$('.show').val 'Hide Answer'
         @element.addClass 'showed'
     else