Merge pull request #2018 from edx/fix/peter/numerical_infinite_bug

Fix infinity bug for numericalresponse; add tests

common/lib/capa/capa/responsetypes.py

@@ -2,7 +2,8 @@
 # File:   courseware/capa/responsetypes.py
 #
 '''
-Problem response evaluation.  Handles checking of student responses, of a variety of types.
+Problem response evaluation.  Handles checking of student responses,
+of a variety of types.
 
 Used by capa_problem.py
 '''
@@ -35,7 +36,7 @@ from datetime import datetime
 from .util import *
 from lxml import etree
 from lxml.html.soupparser import fromstring as fromstring_bs     # uses Beautiful Soup!!! FIXME?
-import xqueue_interface
+import capa.xqueue_interface
 
 log = logging.getLogger(__name__)
 
@@ -300,7 +301,7 @@ class LoncapaResponse(object):
                     # response
                     aid = self.answer_ids[-1]
                     new_cmap.set_hint_and_mode(aid, hint_text, hintmode)
-            log.debug('after hint: new_cmap = %s' % new_cmap)
+            log.debug('after hint: new_cmap = %s', new_cmap)
 
     @abc.abstractmethod
     def get_score(self, student_answers):
@@ -790,6 +791,10 @@ class OptionResponse(LoncapaResponse):
 
 
 class NumericalResponse(LoncapaResponse):
+    '''
+    This response type expects a number or formulaic expression that evaluates
+    to a number (e.g. `4+5/2^2`), and accepts with a tolerance.
+    '''
 
     response_tag = 'numericalresponse'
     hint_tag = 'numericalhint'
@@ -806,12 +811,12 @@ class NumericalResponse(LoncapaResponse):
                 '//*[@id=$id]//responseparam[@type="tolerance"]/@default',
                 id=xml.get('id'))[0]
             self.tolerance = contextualize_text(self.tolerance_xml, context)
-        except Exception:
+        except IndexError:  # xpath found an empty list, so (...)[0] is the error
             self.tolerance = '0'
         try:
             self.answer_id = xml.xpath('//*[@id=$id]//textline/@id',
                                        id=xml.get('id'))[0]
-        except Exception:
+        except IndexError:  # Same as above
             self.answer_id = None
 
     def get_score(self, student_answers):
@@ -836,7 +841,6 @@ class NumericalResponse(LoncapaResponse):
         except:
             # Use the traceback-preserving version of re-raising with a
             # different type
-            import sys
             type, value, traceback = sys.exc_info()
 
             raise StudentInputError, ("Could not interpret '%s' as a number" %
@@ -1869,8 +1873,6 @@ class FormulaResponse(LoncapaResponse):
                 log.debug('formularesponse: error %s in formula' % err)
                 raise StudentInputError("Invalid input: Could not parse '%s' as a formula" %
                                         cgi.escape(given))
-            if numpy.isnan(student_result) or numpy.isinf(student_result):
-                return "incorrect"
             if not compare_with_tolerance(student_result, instructor_result, self.tolerance):
                 return "incorrect"
         return "correct"

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

@@ -438,6 +438,43 @@ class FormulaResponseTest(ResponseTest):
             self.assert_grade(problem, incorrect, 'incorrect',
                               msg="Failed on function {0}; the given, incorrect answer was {1} but graded 'correct'".format(func, incorrect))
 
+    def test_grade_infinity(self):
+        # This resolves a bug where a problem with relative tolerance would
+        # pass with any arbitrarily large student answer.
+
+        sample_dict = {'x': (1, 2)}
+
+        # Test problem
+        problem = self.build_problem(sample_dict=sample_dict,
+                                     num_samples=10,
+                                     tolerance="1%",
+                                     answer="x")
+        # Expect such a large answer to be marked incorrect
+        input_formula = "x*1e999"
+        self.assert_grade(problem, input_formula, "incorrect")
+        # Expect such a large negative answer to be marked incorrect
+        input_formula = "-x*1e999"
+        self.assert_grade(problem, input_formula, "incorrect")
+
+    def test_grade_nan(self):
+        # Attempt to produce a value which causes the student's answer to be
+        # evaluated to nan. See if this is resolved correctly.
+
+        sample_dict = {'x': (1, 2)}
+
+        # Test problem
+        problem = self.build_problem(sample_dict=sample_dict,
+                                     num_samples=10,
+                                     tolerance="1%",
+                                     answer="x")
+        # Expect an incorrect answer (+ nan) to be marked incorrect
+        # Right now this evaluates to 'nan' for a given x (Python implementation-dependent)
+        input_formula = "10*x + 0*1e999"
+        self.assert_grade(problem, input_formula, "incorrect")
+        # Expect an correct answer (+ nan) to be marked incorrect
+        input_formula = "x + 0*1e999"
+        self.assert_grade(problem, input_formula, "incorrect")
+
 
 class StringResponseTest(ResponseTest):
     from response_xml_factory import StringResponseXMLFactory
@@ -714,6 +751,30 @@ class NumericalResponseTest(ResponseTest):
         incorrect_responses = ["", "4.5", "3.5", "0"]
         self.assert_multiple_grade(problem, correct_responses, incorrect_responses)
 
+    def test_grade_infinity(self):
+        # This resolves a bug where a problem with relative tolerance would
+        # pass with any arbitrarily large student answer.
+        problem = self.build_problem(question_text="What is 2 + 2 approximately?",
+                                     explanation="The answer is 4",
+                                     answer=4,
+                                     tolerance="10%")
+        correct_responses = []
+        incorrect_responses = ["1e999", "-1e999"]
+        self.assert_multiple_grade(problem, correct_responses, incorrect_responses)
+
+    def test_grade_nan(self):
+        # Attempt to produce a value which causes the student's answer to be
+        # evaluated to nan. See if this is resolved correctly.
+        problem = self.build_problem(question_text="What is 2 + 2 approximately?",
+                                     explanation="The answer is 4",
+                                     answer=4,
+                                     tolerance="10%")
+        correct_responses = []
+        # Right now these evaluate to `nan`
+        # `4 + nan` should be incorrect
+        incorrect_responses = ["0*1e999", "4 + 0*1e999"]
+        self.assert_multiple_grade(problem, correct_responses, incorrect_responses)
+
     def test_grade_with_script(self):
         script_text = "computed_response = math.sqrt(4)"
         problem = self.build_problem(question_text="What is sqrt(4)?",

common/lib/capa/capa/util.py

@@ -1,4 +1,5 @@
 from .calc import evaluator, UndefinedVariable
+from cmath import isinf
 
 #-----------------------------------------------------------------------------
 #
@@ -20,7 +21,14 @@ def compare_with_tolerance(v1, v2, tol):
         tolerance = tolerance_rel * max(abs(v1), abs(v2))
     else:
         tolerance = evaluator(dict(), dict(), tol)
-    return abs(v1 - v2) <= tolerance
+
+    if isinf(v1) or isinf(v2):
+        # If an input is infinite, we can end up with `abs(v1-v2)` and
+        # `tolerance` both equal to infinity. Then, below we would have
+        # `inf <= inf` which is a fail. Instead, compare directly.
+        return v1 == v2
+    else:
+        return abs(v1 - v2) <= tolerance
 
 
 def contextualize_text(text, context):  # private
@@ -51,7 +59,8 @@ def convert_files_to_filenames(answers):
     new_answers = dict()
     for answer_id in answers.keys():
         answer = answers[answer_id]
-        if is_list_of_files(answer):   # Files are stored as a list, even if one file
+        # Files are stored as a list, even if one file
+        if is_list_of_files(answer):
             new_answers[answer_id] = [f.name for f in answer]
         else:
             new_answers[answer_id] = answers[answer_id]