Fixed issue with E not parsing in preview, when using LaTeX (#241)

* Fixed issue with E not parsing in preview, when using LaTeX

* Added that the case of `e` gets retained on replacement

* Added tests for multicharacter symbols not starting with E

Author: m-messer

app/evaluation_tests.py

@@ -168,6 +168,29 @@ def test_multi_character_implicit_multi_variable(self):
         result = evaluation_function(response_implicit_no_bracket, answer, params)
         assert result["is_correct"] is True, "Response: a/bcd"
 
+    @pytest.mark.parametrize(
+        "response, is_latex, is_correct", [
+            ("e**ea", False, True),
+            ("e**Ea", False, True),
+            ("e^{ea}", True, True),
+            ("e^{Ea}", True, True),
+        ]
+    )
+    def test_e_latex(self, response, is_latex, is_correct):
+        params = {
+            "is_latex": is_latex,
+            "strict_syntax": False,
+            "elementary_functions": True,
+            "symbols": {
+                "ea": {"aliases": ["ea", "Ea"], "latex": "ea"},
+            },
+        }
+        answer = "e**ea"
+
+        result = evaluation_function(response, answer, params)
+        assert result["is_correct"] == is_correct
+
+
 
     def test_mu_preview_evaluate(self):
         response = "10 μA"

app/preview_tests.py

@@ -101,10 +101,10 @@ def test_natural_logarithm_notation(self):
             ("e^{0}", True, True, "e^{0}", "1"),
             ("exp(2)", False, True, "e^{2}", "exp(2)"),
             ("e**2", False, True, "e^{2}", "E**2"),
-            ("e^{2}", True, True, "e^{2}", "exp(2)"),
+            ("e^{2}", True, True, "e^{2}", "E**2"),
             ("exp(x)", False, True, "e^{x}", "exp(x)"),
             ("e**x", False, True, "e^{x}", "E**x"),
-            ("e^{x}", True, True, "e^{x}", "exp(x)")
+            ("e^{x}", True, True, "e^{x}", "E**x")
         ]
     )
     def test_eulers_number_notation(self, response, is_latex, elementary_functions, response_latex, response_sympy):
@@ -116,6 +116,34 @@ def test_eulers_number_notation(self, response, is_latex, elementary_functions,
         assert preview["latex"] == response_latex
         assert preview["sympy"] == response_sympy
 
+    @pytest.mark.parametrize(
+        "response, is_latex, response_latex, response_sympy, symbols", [
+            ("e**ea", False, "e^{ea}", "E**ea", {"ea": {"aliases": ["ea", "Ea"], "latex": "ea"}}),
+            ("e**Ea", False, "e^{ea}", "E**ea", {"ea": {"aliases": ["ea", "Ea"], "latex": "ea"}}),
+            ("e^{ea}", True, "e^{ea}", "e**ea", {"ea": {"aliases": ["ea", "Ea"], "latex": "ea"}}),
+            # ("e^{Ea}", True, "e^{Ea}", "e**ea", {"ea": {"aliases": ["ea", "Ea"], "latex": "ea"}}), # TODO: Clarify if we want to be able to use aliases for LaTeX?
+            ("e**aea", False, "e^{aea}", "E**aea", {"aea": {"aliases": ["aea", "aEa"], "latex": "aea"}}),
+            ("e**aEa", False, "e^{aea}", "E**aea", {"aea": {"aliases": ["aea", "aEa"], "latex": "aea"}}),
+            ("e^{aea}", True, "e^{aea}", "e**aea", {"aea": {"aliases": ["aea", "aEa"], "latex": "aea"}}),
+            # ("e^{aEa}", True, "e^{aEa}", "e**aea", {"aea": {"aliases": ["aea", "aEa"], "latex": "aea"}}), # TODO: Clarify if we want to be able to use aliases for LaTeX?
+        ]
+    )
+    def test_e_latex(self, response, is_latex, response_latex, response_sympy, symbols):
+        params = {
+            "is_latex": is_latex,
+            "strict_syntax": False,
+            "elementary_functions": True,
+            "symbols": symbols,
+        }
+
+        result = preview_function(response, params)
+        assert "preview" in result.keys()
+        preview = result["preview"]
+
+        assert preview["latex"] == response_latex
+        assert preview["sympy"] == response_sympy
+
+
     @pytest.mark.parametrize(
         "response, is_latex, response_latex, response_sympy",
         [
@@ -199,5 +227,6 @@ def test_multi_character_implicit_multi_variable(self):
         assert result["preview"]["latex"] =='\\frac{a}{bc \\cdot d}'
         assert result["preview"]["sympy"] == "a/bcd"
 
+
 if __name__ == "__main__":
     pytest.main(['-xk not slow', "--tb=line", os.path.abspath(__file__)])

app/utility/preview_utilities.py

@@ -37,31 +37,72 @@ def find_placeholder(exp):
         if char not in exp:
             return char
 
-def preprocess_E(latex_str: str, placeholder: str) -> str:
+
+def preprocess_E(latex_str: str) -> tuple[str, dict[str, str]]:
     """
-    Replace all symbols starting with 'E' (including plain 'E') with a
-    placeholder, so latex2sympy does not interpret 'E' as Euler's number.
+    Replace all symbols starting with 'E' or 'e' with placeholders,
+    so latex2sympy does not interpret 'E' as Euler's number.
+    Returns the modified string and a dict mapping replaced chars to their placeholders.
     """
-    # Replace E, E_x, ER_2, Efield, etc.
+    replacements = {}
+
+    # Find placeholder for uppercase E if needed
+    if re.search(r'(?<!\\)E(?:[a-zA-Z_][a-zA-Z0-9_]*|_\{[^}]*\})?', latex_str):
+        placeholder_E = find_placeholder(latex_str)
+        if placeholder_E:
+            replacements['E'] = placeholder_E
+
+    # Find placeholder for lowercase e if needed (exclude already used placeholder)
+    if re.search(r'(?<!\\)e(?:[a-zA-Z_][a-zA-Z0-9_]*|_\{[^}]*\})?', latex_str):
+        used_chars = latex_str + ''.join(replacements.values())
+        placeholder_e = find_placeholder(used_chars)
+        if placeholder_e:
+            replacements['e'] = placeholder_e
+
+    # If no replacements needed, return original string
+    if not replacements:
+        return latex_str, {}
+
+    # Replace E and e with their respective placeholders
     def repl(match):
         token = match.group(0)
-        return placeholder + token[1:]
+        first_char = token[0]
+        if first_char in replacements:
+            return replacements[first_char] + token[1:]
+        return token
+
+    # Match E or e followed by optional alphanumeric/underscore (including within braces)
+    pattern = re.compile(r'(?<!\\)[Ee](?:[a-zA-Z_][a-zA-Z0-9_]*|_\{[^}]*\})?')
+    modified_str = pattern.sub(repl, latex_str)
 
-    # Match E followed by optional subscript or alphanumeric/underscore
-    pattern = re.compile(r'(?<![\\a-zA-Z])E([A-Za-z0-9_]*(?:_\{[^}]*\})?)')
-    return pattern.sub(repl, latex_str)
+    # Return the modified string and the replacements dict
+    return modified_str, replacements
 
 
-def postprocess_E(expr, placeholder):
+def postprocess_E(expr, replacements):
     """
-    Replace all placeholder symbols back to symbols starting with E.
+    Replace all placeholder symbols back to symbols starting with E or e.
+
+    Args:
+        expr: The sympy expression
+        replacements: Dict mapping original chars ('E', 'e') to their placeholders
     """
+    if not replacements:
+        return expr
+
+    # Create reverse mapping: placeholder -> original char
+    placeholder_to_char = {v: k for k, v in replacements.items()}
+
     subs = {}
     for s in expr.free_symbols:
         name = str(s)
-        if name.startswith(placeholder):
-            new_name = "E" + name[len(placeholder):]
-            subs[s] = Symbol(new_name)
+        # Check if this symbol starts with any of our placeholders
+        for placeholder, original_char in placeholder_to_char.items():
+            if name.startswith(placeholder):
+                new_name = original_char + name[len(placeholder):]
+                subs[s] = Symbol(new_name)
+                break  # Only replace once per symbol
+
     return expr.xreplace(subs)
 
 
@@ -121,25 +162,28 @@ def parse_latex(response: str, symbols: SymbolDict, simplify: bool, parameters=N
 
         if "\pm" not in symbol_str and "\mp" not in symbol_str:
             try:
-                latex_symbol = latex2sympy(latex_symbol_str)
+                latex_symbol_str_preprocessed, replacements = preprocess_E(latex_symbol_str)
+                latex_symbol_parsed = latex2sympy(latex_symbol_str_preprocessed)
+                latex_symbol_str_postprocess = postprocess_E(latex_symbol_parsed, replacements)
+
             except Exception:
                 raise ValueError(
                     f"Couldn't parse latex symbol {latex_symbol_str} "
                     f"to sympy symbol."
                 )
-            substitutions[latex_symbol] = Symbol(sympy_symbol_str)
+            substitutions[latex_symbol_str_postprocess] = Symbol(sympy_symbol_str)
+
 
     parsed_responses = set()
     for expression in response_set:
         try:
-            e_placeholder = find_placeholder(expression)
 
-            expression_preprocessed = preprocess_E(expression, e_placeholder)
+            expression_preprocessed, replacements = preprocess_E(expression)
             expression_parsed = latex2sympy(expression_preprocessed, substitutions)
             if isinstance(expression_parsed, list):
                 expression_parsed = expression_parsed.pop()
 
-            expression_postprocess = postprocess_E(expression_parsed, e_placeholder)
+            expression_postprocess = postprocess_E(expression_parsed, replacements)
             if simplify is True:
                 expression_postprocess = expression_postprocess.simplify()
         except Exception as e: