Expand SymPy locals via safe filtered allowlist

README.md

@@ -377,6 +377,7 @@ If you get stuck, run `:examples` or `:h`.
 - In ODE input, prefer explicit multiplication (`20*y` instead of `20y`) for predictable parsing.
 - Common LaTeX wrappers and commands are normalized: `$...$`, `\(...\)`, `\sin`, `\cos`, `\ln`, `\sqrt{...}`, `\frac{a}{b}`
 - `name = expr` assigns in REPL session (`ans` is always last result)
+- Built-in helper names are reserved for evaluation (for example `sin`, `gamma`, `atan2`, `I`) and cannot be reassigned.
 - Undefined symbols raise an error
 
 ## Safety limits

src/calc/core.py

@@ -4,6 +4,7 @@
 from difflib import get_close_matches
 from math import log
 
+import sympy as _sympy
 from sympy import (
     Abs,
     Add,
@@ -50,7 +51,7 @@
     function_exponentiation,
     implicit_multiplication_application,
     parse_expr,
-    rationalize, 
+    rationalize,
 )
 
 x, y, z, t = symbols("x y z t")
@@ -131,6 +132,56 @@ def _den(expr):
     "S": Symbol,
 }
 
+SYMPY_EXTRA_ALLOWLIST = (
+    "I",
+    "acos",
+    "acosh",
+    "apart",
+    "asin",
+    "asinh",
+    "atan",
+    "atan2",
+    "atanh",
+    "binomial",
+    "cancel",
+    "collect",
+    "cosh",
+    "cot",
+    "csc",
+    "expand",
+    "factor",
+    "gamma",
+    "limit",
+    "powsimp",
+    "product",
+    "sec",
+    "series",
+    "sinh",
+    "summation",
+    "tanh",
+    "together",
+    "trigsimp",
+)
+
+
+def _expanded_sympy_locals() -> dict[str, object]:
+    expanded: dict[str, object] = {}
+    for name in SYMPY_EXTRA_ALLOWLIST:
+        if name in LOCALS_DICT:
+            continue
+        if not name.isidentifier() or name.startswith("_"):
+            continue
+        value = getattr(_sympy, name, None)
+        if value is None:
+            continue
+        if not (callable(value) or isinstance(value, _sympy.Basic)):
+            continue
+        expanded[name] = value
+    return expanded
+
+
+LOCALS_DICT.update(_expanded_sympy_locals())
+
 
 # parse_expr internally uses eval. Keep globals minimal and disable builtins.
 GLOBAL_DICT = {
@@ -145,14 +196,14 @@ def _den(expr):
     "factorial": factorial,
 }
 
-TRANSFORMS = (auto_number, factorial_notation, convert_xor, function_exponentiation, rationalize, )
+TRANSFORMS = (auto_number, factorial_notation, convert_xor, function_exponentiation, rationalize)
 RELAXED_TRANSFORMS = (
     auto_number,
     factorial_notation,
     convert_xor,
     function_exponentiation,
     implicit_multiplication_application,
-    rationalize, 
+    rationalize,
 )
 MAX_EXPRESSION_CHARS = 2000
 BLOCKED_PATTERN = re.compile(r"(__|;|\n|\r)")

tests/test_core.py

@@ -1,6 +1,7 @@
 import pytest
+from sympy import I, Symbol
 
-from calc.core import evaluate, normalize_expression, reserved_name_suggestion
+from calc.core import LOCALS_DICT, evaluate, normalize_expression, reserved_name_suggestion
 
 
 def test_exact_arithmetic():
@@ -135,6 +136,20 @@ def test_symbol_helpers_for_coefficient_workflows():
     assert "C: 421/15" in out
 
 
+def test_expanded_sympy_allowlist_functions_are_available():
+    assert str(evaluate("binomial(5, 2)")) == "10"
+    assert str(evaluate("gamma(6)")) == "120"
+    assert str(evaluate("limit(sin(x)/x, x, 0)")) == "1"
+    assert str(evaluate("atan2(1, 1)")) == "pi/4"
+    assert str(evaluate("I^2")) == "-1"
+
+
+def test_expanded_sympy_allowlist_does_not_override_curated_names():
+    assert LOCALS_DICT["S"] is Symbol
+    assert str(evaluate('S("A")')) == "A"
+    assert LOCALS_DICT["I"] is I
+
+
 def test_numeric_eval():
     assert str(evaluate("N(pi, 10)")) == "3.141592654"
 
@@ -162,6 +177,15 @@ def test_assignment_and_ans_with_session_locals():
 def test_assignment_rejects_reserved_name():
     with pytest.raises(ValueError, match="reserved name"):
         evaluate("sin = 2", session_locals={})
+    with pytest.raises(ValueError, match="reserved name"):
+        evaluate("gamma = 2", session_locals={})
+    with pytest.raises(ValueError, match="reserved name"):
+        evaluate("I = 2", session_locals={})
+
+
+def test_expanded_sympy_allowlist_keeps_local_surface_safe():
+    assert "__builtins__" not in LOCALS_DICT
+    assert all(not name.startswith("_") for name in LOCALS_DICT)
 
 
 def test_reserved_name_suggestion_prefers_close_session_name():