Fixed bug when 'as' was a substring in an expression

E.g. 'a sin(x)' would cause a parse error/ Fixed by changing how substitution of 'as' was handled when 'as' was not an input symbol.

Author: KarlLundengaard

app/expression_utilities.py

@@ -274,10 +274,10 @@ def substitute_input_symbols(exprs, params):
     if lambda_value is not None:
         lambda_value["aliases"].append("lambda")
     input_symbols.update({"lamda": lambda_value})
-    as_value = input_symbols.pop("as", {"latex": r"as", "aliases": ["as"]})
+    as_value = input_symbols.pop("as", None)
     if as_value is not None:
         as_value["aliases"].append("as")
-        input_symbols.update({"a s": as_value})
+        input_symbols.update({"a*s": as_value})
     params.update({"symbols": input_symbols})
 
     for (code, symbol_data) in input_symbols.items():
@@ -618,7 +618,7 @@ def parse_expression(expr, parsing_params):
     unsplittable_symbols = parsing_params.get("unsplittable_symbols", ())
     symbol_dict = parsing_params.get("symbol_dict", {})
     separate_unsplittable_symbols = [(x, " "+x+" ") for x in unsplittable_symbols]
-    # new approach
+
     substitutions = separate_unsplittable_symbols
     if parsing_params.get("elementary_functions", False) is True:
         alias_substitutions = []
@@ -629,6 +629,8 @@ def parse_expression(expr, parsing_params):
                 if alias in expr:
                     alias_substitutions += [(alias, " "+name)]
         substitutions += alias_substitutions
+    # Special substitution to avoid 'as' being a reserved keyword in python
+    substitutions += [("as", "a*s")]
     substitutions.sort(key=lambda x: -len(x[0]))
     expr = substitute(expr, substitutions)
     can_split = lambda x: False if x in unsplittable_symbols else _token_splittable(x)

app/symbolic_comparison_evaluation_tests.py

@@ -1536,5 +1536,27 @@ def test_as_in_input_symbols(self):
         result = evaluation_function(response, answer, params)
         assert result["is_correct"] is True
 
+    def test_as_substring_in_expression(self):
+        params = {
+            "strict_syntax": False,
+            "elementary_functions": True,
+        }
+
+        response = "asin(omega t)"
+
+        answer = "a*sin(omega t)"
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] is False
+
+        answer = "a sin(omega t)"
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] is False
+
+        response = "a*sin(omega t)"
+
+        answer = "sin(omega t)*a"
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] is False
+
 if __name__ == "__main__":
     pytest.main(['-xk not slow', "--tb=line", '--durations=10', os.path.abspath(__file__)])