Allow python variable interpolation in CustomResponse 'expect' and 'answer' attributes

common/lib/capa/capa/responsetypes.py

@@ -2208,7 +2208,7 @@ class CustomResponse(LoncapaResponse):
 
         # if <customresponse> has an "expect" (or "answer") attribute then save
         # that
-        self.expect = xml.get('expect') or xml.get('answer')
+        self.expect = contextualize_text(xml.get('expect') or xml.get('answer'), self.context)
 
         log.debug('answer_ids=%s', self.answer_ids)
 

common/lib/capa/capa/tests/response_xml_factory.py

@@ -264,11 +264,15 @@ class CustomResponseXMLFactory(ResponseXMLFactory):
         *expect*: The value passed to the function cfn
 
         *answer*: Inline script that calculates the answer
+
+        *answer_attr*: The "answer" attribute on the tag itself (treated as an
+        alias to "expect", though "expect" takes priority if both are given)
         """
 
         # Retrieve **kwargs
         cfn = kwargs.get('cfn', None)
         expect = kwargs.get('expect', None)
+        answer_attr = kwargs.get('answer_attr', None)
         answer = kwargs.get('answer', None)
         options = kwargs.get('options', None)
         cfn_extra_args = kwargs.get('cfn_extra_args', None)
@@ -282,6 +286,9 @@ class CustomResponseXMLFactory(ResponseXMLFactory):
         if expect:
             response_element.set('expect', str(expect))
 
+        if answer_attr:
+            response_element.set('answer', str(answer_attr))
+
         if answer:
             answer_element = etree.SubElement(response_element, "answer")
             answer_element.text = str(answer)

common/lib/capa/capa/tests/test_responsetypes.py

@@ -1799,6 +1799,33 @@ class CustomResponseTest(ResponseTest):  # pylint: disable=missing-docstring
         self.assertEqual(correct_map.get_npoints('1_2_1'), 0.5)
         self.assertEqual(correct_map.get_correctness('1_2_1'), 'partially-correct')
 
+    def test_script_context(self):
+        # Ensure that python script variables can be used in the "expect" and "answer" fields,
+
+        script = script = textwrap.dedent("""
+            expected_ans = 42
+
+            def check_func(expect, answer_given):
+                return answer_given == expect
+        """)
+
+        problems = (
+            self.build_problem(script=script, cfn="check_func", expect="$expected_ans"),
+            self.build_problem(script=script, cfn="check_func", answer_attr="$expected_ans")
+        )
+
+        input_dict = {'1_2_1': '42'}
+
+        for problem in problems:
+            correctmap = problem.grade_answers(input_dict)
+
+            # CustomResponse also adds 'expect' to the problem context; check that directly first:
+            self.assertEqual(problem.context['expect'], '42')
+
+            # Also make sure the problem was graded correctly:
+            correctness = correctmap.get_correctness('1_2_1')
+            self.assertEqual(correctness, 'correct')
+
     def test_function_code_multiple_input_no_msg(self):
 
         # Check functions also have the option of returning