improve capa error handling a bit - for better user experience

- if no answer given, then symbolicresponse + customrepsonse now
  give an error message, instead of doing nothing
- in capa_module if lcp.grade_answers fails, in DEBUG mode display
  alert with useful error message

common/lib/capa/capa_problem.py

@@ -304,7 +304,8 @@ class LoncapaProblem(object):
             try:
                 exec code in context, context        	# use "context" for global context; thus defs in code are global within code
             except Exception:
-                log.exception("Error while execing code: " + code)
+                log.exception("Error while execing script code: " + code)
+                raise responsetypes.LoncapaProblemError("Error while executing script code")
         return context
 
     def _extract_html(self, problemtree):  # private

common/lib/capa/responsetypes.py

@@ -567,7 +567,7 @@ def sympy_check2():
 
         # if there is only one box, and it's empty, then don't evaluate
         if len(idset)==1 and not submission[0]:
-            return {idset[0]:'no_answer_entered'}
+            return CorrectMap(idset[0],'incorrect',msg='<font color="red">No answer entered!</font>')
 
         correct = ['unknown'] * len(idset)
         messages = [''] * len(idset)

common/lib/xmodule/capa_module.py

@@ -409,18 +409,21 @@ class Module(XModule):
             correct_map = self.lcp.grade_answers(answers)
         except StudentInputError as inst:
             # TODO (vshnayder): why is this line here?
-            self.lcp = LoncapaProblem(self.filestore.open(self.filename),
-                                      id=lcp_id, state=old_state, system=self.system)
+            #self.lcp = LoncapaProblem(self.filestore.open(self.filename),
+            #                          id=lcp_id, state=old_state, system=self.system)
             traceback.print_exc()
             return {'success': inst.message}
-        except:
+        except Exception, err:
             # TODO: why is this line here?
-            self.lcp = LoncapaProblem(self.filestore.open(self.filename),
-                                      id=lcp_id, state=old_state, system=self.system)
+            #self.lcp = LoncapaProblem(self.filestore.open(self.filename),
+            #                          id=lcp_id, state=old_state, system=self.system)
+            if self.DEBUG:
+                msg = "Error checking problem: " + str(err)
+                msg += '\nTraceback:\n' + traceback.format_exc()
+                return {'success':msg}
+                
             traceback.print_exc()
             raise Exception,"error in capa_module"
-            # TODO: Dead code...  is this a bug, or just old?
-            return {'success':'Unknown Error'}
 
         self.attempts = self.attempts + 1
         self.lcp.done = True

common/lib/xmodule/seq_module.py

@@ -77,6 +77,7 @@ class Module(XModule):
             contents['progress_status'] = Progress.to_js_status_str(progress)
             contents['progress_detail'] = Progress.to_js_detail_str(progress)
 
+        content = None
         for (content, element_class) in zip(self.contents, child_classes):
             new_class = 'other'
             for c in class_priority: