Enabled ruff rule RUF012

Author: Spaarsh

pyproject.toml

@@ -91,7 +91,7 @@ ignore = [
     "TRY003",
     # "B904",
     # "UP006",
-    "RUF012",
+    # "RUF012",
     "FBT003",
     "C416",
     "SIM102",

python/datafusion/expr.py

@@ -22,7 +22,7 @@
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Any, Optional
+from typing import TYPE_CHECKING, Any, ClassVar, Optional
 
 import pyarrow as pa
 
@@ -439,7 +439,7 @@ def fill_null(self, value: Any | Expr | None = None) -> Expr:
             value = Expr.literal(value)
         return Expr(functions_internal.nvl(self.expr, value.expr))
 
-    _to_pyarrow_types = {
+    _to_pyarrow_types: ClassVar[dict[type, pa.DataType]] = {
         float: pa.float64(),
         int: pa.int64(),
         str: pa.string(),