Make type check for self.code a little more robust, give default val for mmlans…

Make type check for self.code a little more robust, give default val for mmlans so it's never undefined

common/lib/capa/capa/responsetypes.py

@@ -999,7 +999,7 @@ def sympy_check2():
         self.context['debug'] = self.system.DEBUG
 
         # exec the check function
-        if type(self.code) == str:
+        if isinstance(self.code, basestring):
             try:
                 exec self.code in self.context['global_context'], self.context
                 correct = self.context['correct']

lms/lib/symmath/symmath_check.py

@@ -238,8 +238,7 @@ def symmath_check(expect, ans, dynamath=None, options=None, debug=None, xml=None
     ###### PMathML input ######
     # convert mathml answer to formula
     try:
-        if dynamath:
-            mmlans = dynamath[0]
+        mmlans = dynamath[0] if dynamath else None
     except Exception, err:
         mmlans = None
     if not mmlans: