Merge pull request RustPython#5184 from youknowone/symboltable

better symboltable error message

Author: youknowone

compiler/codegen/src/compile.rs

@@ -478,8 +478,8 @@ impl Compiler {
         self.check_forbidden_name(&name, usage)?;
 
         let symbol_table = self.symbol_table_stack.last().unwrap();
-        let symbol = symbol_table.lookup(name.as_ref()).expect(
-            "The symbol must be present in the symbol table, even when it is undefined in python.",
+        let symbol = symbol_table.lookup(name.as_ref()).unwrap_or_else(||
+            panic!("The symbol '{name}' must be present in the symbol table, even when it is undefined in python."),
         );
         let info = self.code_stack.last_mut().unwrap();
         let mut cache = &mut info.name_cache;