gh-143504: Expose CELL status of a symbol in symtable

Lib/symtable.py

@@ -184,6 +184,7 @@ class Function(SymbolTable):
     __frees = None
     __globals = None
     __nonlocals = None
+    __cells = None
 
     def __idents_matching(self, test_func):
         return tuple(ident for ident in self.get_identifiers()
@@ -230,8 +231,11 @@ def get_frees(self):
         return self.__frees
 
     def get_cells(self):
-        """Return a list of cell variable names in the table."""
-        return [s.get_name() for s in self.get_symbols() if s.is_cell()]
+        """Return a list of cell variable names in the table.
+        """
+        if self.__cells is None:
+            self.__cells = [s.get_name() for s in self.get_symbols() if s.is_cell()]
+        return self.__cells
 
 
 class Class(SymbolTable):

Lib/test/test_symtable.py

@@ -285,18 +285,8 @@ def test_free(self):
         self.assertTrue(self.internal.lookup("x").is_free())
 
     def test_cells(self):
-        #test for addition of is_cell() and get_cells()
-        #see https://github.com/python/cpython/issues/143504
-        code="""def outer():
-                    x=1
-                    def inner():
-                        return x"""
-
-        top=symtable.symtable(code,"?","exec")
-        outer = find_block(top, "outer")
-        self.assertIn("x",outer.get_cells())
-        self.assertTrue(outer.lookup("x").is_cell())
-        self.assertFalse(outer.lookup("inner").is_cell())
+        self.assertTrue(self.spam.lookup("x").is_cell())
+
 
     def test_referenced(self):
         self.assertTrue(self.internal.lookup("x").is_referenced())