Fix TypeError when the answer or response is an inequality

app/context/symbolic.py

@@ -1,6 +1,8 @@
 from copy import deepcopy
 from sympy import Add, Pow, Mul, Equality, pi, im, I, N, oo
 from sympy import re as real_part
+from sympy.core.relational import Relational
+from sympy.logic.boolalg import BooleanAtom
 
 from ..utility.expression_utilities import (
     default_parameters,
@@ -115,12 +117,21 @@ def do_comparison(comparison_symbol, expression):
     return result
 
 
+def is_inequality_or_boolean(expr):
+    # Inequalities (e.g. 8 < 9) and booleans (e.g. 5 < 1.43 evaluated to False) are not supported
+    # and cannot be subtracted, so they cannot be compared like other expressions.
+    # NOTE: Not checking for Boolean, since Symbol is a subclass of Boolean.
+    return isinstance(expr, (Relational, BooleanAtom)) and not isinstance(expr, Equality)
+
+
 def check_equality(criterion, parameters_dict, local_substitutions=[]):
     lhs_expr, rhs_expr = create_expressions_for_comparison(criterion, parameters_dict, local_substitutions)
     if isinstance(lhs_expr, Equality) and not isinstance(rhs_expr, Equality):
         result = False
     elif not isinstance(lhs_expr, Equality) and isinstance(rhs_expr, Equality):
         result = False
+    elif is_inequality_or_boolean(lhs_expr) or is_inequality_or_boolean(rhs_expr):
+        result = False
     else:
         try:
             either_is_infinite = lhs_expr.is_infinite or rhs_expr.is_infinite

app/evaluation.py

@@ -9,6 +9,7 @@
 from .utility.evaluation_result_utilities import EvaluationResult
 from .utility.preview_utilities import parse_latex
 from .context.symbolic import context as symbolic_context
+from .context.symbolic import is_inequality_or_boolean
 from .context.physical_quantity import context as quantity_context
 from .feedback.symbolic import feedback_generators as symbolic_feedback_string_generators
 
@@ -33,7 +34,10 @@ class EvaluationError(Exception):
 
 
 messages = {
-    "RESERVED_EXPRESSION_MISSING": lambda label: f"Reserved expression `{label}` is not defined."
+    "RESERVED_EXPRESSION_MISSING": lambda label: f"Reserved expression `{label}` is not defined.",
+    "RESERVED_EXPRESSION_INEQUALITY": lambda label: (
+        f"Reserved expression `{label}` is an inequality or evaluates to true/false, which is not supported."
+    )
 }
 
 
@@ -174,6 +178,11 @@ def parse_reserved_expressions(reserved_expressions, parameters, result):
                         )
                     else:
                         raise TaskConfigurationError(symbolic_comparison_internal_messages("PARSE_ERROR")({'x': expr})) from e
+                if key == "task" and is_inequality_or_boolean(expr_parsed):
+                    raise TaskConfigurationError(
+                        messages["RESERVED_EXPRESSION_INEQUALITY"](label),
+                        f"RESERVED_EXPRESSION_INEQUALITY_{label}"
+                    )
             reserved_expressions_dict[key].update({label: expr_parsed})
     return success, reserved_expressions_dict
 

app/tests/symbolic_evaluation_test.py

@@ -1,7 +1,7 @@
 import pytest
 import os
 
-from ..evaluation import evaluation_function
+from ..evaluation import TaskConfigurationError, evaluation_function
 from ..utility.expression_utilities import elementary_functions_names, substitute
 
 # REMARK: If a case is marked with an alternative output, this means that it is difficult in this case to prevent sympy from simplifying for that particular case
@@ -2144,7 +2144,29 @@ def test_equality_with_both_sides_equal_in_response(self):
         }
         result = evaluation_function(response, answer, params)
         assert result["is_correct"] is False
-
+
+    @pytest.mark.parametrize("response", ["8<9", "x<8", "8>=8", "8<5"])
+    def test_inequality_response_is_incorrect(self, response):
+        answer = "8"
+        params = {
+            "strict_syntax": False,
+            "elementary_functions": True,
+            "relative_tolerance": 0.0005,
+        }
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] is False
+
+    @pytest.mark.parametrize("answer", ["5<1.43", "x<8"])
+    def test_inequality_answer_is_task_configuration_error(self, answer):
+        response = "5<1.43"
+        params = {
+            "strict_syntax": False,
+            "elementary_functions": True,
+        }
+        with pytest.raises(TaskConfigurationError) as e:
+            evaluation_function(response, answer, params)
+        assert "`answer` is an inequality" in str(e.value)
+
     def test_integral(self):
         response = "6y"
         answer = "int(3*x*y, (x, 0, 2))"