for between_comparer, ensure input is real

mitxgraders/comparers/comparers.py

@@ -45,6 +45,7 @@
 """
 from numbers import Number
 import numpy as np
+from mitxgraders.exceptions import InputTypeError
 
 def equality_comparer(comparer_params_evals, student_eval, utils):
     """
@@ -80,9 +81,18 @@ def between_comparer(comparer_params_evals, student_eval, utils):
     False
     >>> grader(None, '5e7')['ok']
     True
+
+    Input must be real:
+    >>> grader(None, '5e8+2e6*i')['ok']
+    Traceback (most recent call last):
+    InputTypeError: Input must be real.
+
     """
     start, stop = comparer_params_evals
 
+    if not np.isreal(student_eval):
+        raise InputTypeError("Input must be real.")
+
     return start <= student_eval <= stop
 
 def congruence_comparer(comparer_params_evals, student_eval, utils):

mitxgraders/exceptions.py

@@ -39,6 +39,12 @@ class InvalidInput(StudentFacingError):
     """
     pass
 
+class InputTypeError(InvalidInput):
+    """
+    Indicates that student's input has evaluated to an object of the wrong
+    type (or shape).
+    """
+
 class MissingInput(StudentFacingError):
     """
     Raised when a required input has been left blank.

mitxgraders/formulagrader/matrixgrader.py

@@ -6,6 +6,7 @@
 from numbers import Number
 from collections import namedtuple
 from voluptuous import Required, Any
+from mitxgraders.exceptions import InputTypeError
 from mitxgraders.formulagrader.formulagrader import FormulaGrader
 from mitxgraders.helpers.validatorfuncs import NonNegative
 from mitxgraders.helpers.calc import MathArray, within_tolerance, identity
@@ -14,12 +15,6 @@
 from mitxgraders.helpers.calc.mathfuncs import (
     merge_dicts, ARRAY_ONLY_FUNCTIONS)
 
-class InputTypeError(CalcError):
-    """
-    Indicates that student's input has evaluated to an object of the wrong
-    type (or shape).
-    """
-
 class MatrixGrader(FormulaGrader):
     """
     An extension of FormulaGrader with better support for grading expressions