diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 1f50558c..51e34355 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -30,7 +30,7 @@ repos:
     hooks:
       - id: clang-format
   - repo: https://github.com/astral-sh/ruff-pre-commit
-    rev: v0.8.3
+    rev: v0.8.4
     hooks:
       - id: ruff
         args: [--fix, --exit-non-zero-on-fix]
@@ -39,7 +39,7 @@ repos:
     hooks:
       - id: black
   - repo: https://github.com/asottile/pyupgrade
-    rev: v3.19.0
+    rev: v3.19.1
     hooks:
       - id: pyupgrade
         args: [--py38-plus]
diff --git a/optree/integration/__init__.py b/optree/integration/__init__.py
index afc4753e..f844214d 100644
--- a/optree/integration/__init__.py
+++ b/optree/integration/__init__.py
@@ -32,7 +32,7 @@ def __dir__() -> list[str]:
     return [*sorted(SUBMODULES), 'SUBMODULES']
 
 
-def __getattr__(name: str) -> ModuleType:
+def __getattr__(name: str, /) -> ModuleType:
     if name in SUBMODULES:
         import importlib  # pylint: disable=import-outside-toplevel
         import sys  # pylint: disable=import-outside-toplevel
diff --git a/optree/integration/jax.py b/optree/integration/jax.py
index c57ebd7d..abe8336b 100644
--- a/optree/integration/jax.py
+++ b/optree/integration/jax.py
@@ -35,8 +35,8 @@
 
 import contextlib
 import itertools
-import operator
 import warnings
+from operator import itemgetter
 from types import FunctionType
 from typing import Any, Callable
 from typing_extensions import TypeAlias  # Python 3.10+
@@ -66,7 +66,7 @@ class HashablePartial:  # pragma: no cover
     args: tuple[Any, ...]
     kwargs: dict[str, Any]
 
-    def __init__(self, func: FunctionType | HashablePartial, *args: Any, **kwargs: Any) -> None:
+    def __init__(self, func: FunctionType | HashablePartial, /, *args: Any, **kwargs: Any) -> None:
         """Construct a :class:`HashablePartial` instance."""
         if not callable(func):
             raise TypeError(f'Expected a callable, got {func!r}.')
@@ -82,23 +82,23 @@ def __init__(self, func: FunctionType | HashablePartial, *args: Any, **kwargs: A
         else:
             raise TypeError(f'Expected a function, got {func!r}.')
 
-    def __eq__(self, other: object) -> bool:
+    def __eq__(self, other: object, /) -> bool:
         return (
             type(other) is HashablePartial  # pylint: disable=unidiomatic-typecheck
-            and self.func.__code__ == other.func.__code__  # type: ignore[attr-defined]
+            and self.func.__code__ == other.func.__code__
             and (self.args, self.kwargs) == (other.args, other.kwargs)
         )
 
-    def __hash__(self) -> int:
+    def __hash__(self, /) -> int:
         return hash(
             (
-                self.func.__code__,  # type: ignore[attr-defined]
+                self.func.__code__,
                 self.args,
-                tuple(total_order_sorted(self.kwargs.items(), key=operator.itemgetter(0))),
+                tuple(total_order_sorted(self.kwargs.items(), key=itemgetter(0))),
             ),
         )
 
-    def __call__(self, *args: Any, **kwargs: Any) -> Any:
+    def __call__(self, /, *args: Any, **kwargs: Any) -> Any:
         kwargs = {**self.kwargs, **kwargs}
         return self.func(*self.args, *args, **kwargs)
 
@@ -110,6 +110,7 @@ def __call__(self, *args: Any, **kwargs: Any) -> Any:
 
 def tree_ravel(
     tree: ArrayLikeTree,
+    /,
     is_leaf: Callable[[Any], bool] | None = None,
     *,
     none_is_leaf: bool = False,
@@ -193,13 +194,15 @@ def _tree_unravel(
     treespec: PyTreeSpec,
     unravel_flat: Callable[[Array], list[ArrayLike]],
     flat: Array,
+    /,
 ) -> ArrayTree:
     return tree_unflatten(treespec, unravel_flat(flat))
 
 
-def _ravel_leaves(
-    leaves: list[ArrayLike],
-) -> tuple[Array, Callable[[Array], list[ArrayLike]]]:
+def _ravel_leaves(leaves: list[ArrayLike], /) -> tuple[
+    Array,
+    Callable[[Array], list[ArrayLike]],
+]:
     if not leaves:
         return (jnp.zeros(0), _unravel_empty)
 
@@ -229,7 +232,7 @@ def _ravel_leaves(
     )
 
 
-def _unravel_empty(flat: Array) -> list[ArrayLike]:
+def _unravel_empty(flat: Array, /) -> list[ArrayLike]:
     if jnp.shape(flat) != (0,):
         raise ValueError(
             f'The unravel function expected an array of shape {(0,)}, '
@@ -243,6 +246,7 @@ def _unravel_leaves_single_dtype(
     indices: tuple[int, ...],
     shapes: tuple[tuple[int, ...], ...],
     flat: Array,
+    /,
 ) -> list[Array]:
     if jnp.shape(flat) != (indices[-1],):
         raise ValueError(
@@ -260,6 +264,7 @@ def _unravel_leaves(
     from_dtypes: tuple[jnp.dtype, ...],
     to_dtype: jnp.dtype,
     flat: Array,
+    /,
 ) -> list[Array]:
     if jnp.shape(flat) != (indices[-1],):
         raise ValueError(
diff --git a/optree/integration/numpy.py b/optree/integration/numpy.py
index b9609969..f2b29191 100644
--- a/optree/integration/numpy.py
+++ b/optree/integration/numpy.py
@@ -39,6 +39,7 @@
 
 def tree_ravel(
     tree: ArrayLikeTree,
+    /,
     is_leaf: Callable[[Any], bool] | None = None,
     *,
     none_is_leaf: bool = False,
@@ -122,13 +123,15 @@ def _tree_unravel(
     treespec: PyTreeSpec,
     unravel_flat: Callable[[np.ndarray], list[np.ndarray]],
     flat: np.ndarray,
+    /,
 ) -> ArrayTree:
     return tree_unflatten(treespec, unravel_flat(flat))
 
 
-def _ravel_leaves(
-    leaves: list[np.ndarray],
-) -> tuple[np.ndarray, Callable[[np.ndarray], list[np.ndarray]]]:
+def _ravel_leaves(leaves: list[np.ndarray], /) -> tuple[
+    np.ndarray,
+    Callable[[np.ndarray], list[np.ndarray]],
+]:
     if not leaves:
         return (np.zeros(0), _unravel_empty)
 
@@ -155,7 +158,7 @@ def _ravel_leaves(
     )
 
 
-def _unravel_empty(flat: np.ndarray) -> list[np.ndarray]:
+def _unravel_empty(flat: np.ndarray, /) -> list[np.ndarray]:
     if np.shape(flat) != (0,):
         raise ValueError(
             f'The unravel function expected an array of shape {(0,)}, '
@@ -168,6 +171,7 @@ def _unravel_leaves_single_dtype(
     indices: tuple[int, ...],
     shapes: tuple[tuple[int, ...], ...],
     flat: np.ndarray,
+    /,
 ) -> list[np.ndarray]:
     if np.shape(flat) != (indices[-1],):
         raise ValueError(
@@ -185,6 +189,7 @@ def _unravel_leaves(
     from_dtypes: tuple[np.dtype, ...],
     to_dtype: np.dtype,
     flat: np.ndarray,
+    /,
 ) -> list[np.ndarray]:
     if np.shape(flat) != (indices[-1],):
         raise ValueError(
diff --git a/optree/integration/torch.py b/optree/integration/torch.py
index 6af98c22..cd4c078a 100644
--- a/optree/integration/torch.py
+++ b/optree/integration/torch.py
@@ -36,6 +36,7 @@
 
 def tree_ravel(
     tree: TensorTree,
+    /,
     is_leaf: Callable[[Any], bool] | None = None,
     *,
     none_is_leaf: bool = False,
@@ -119,13 +120,15 @@ def _tree_unravel(
     treespec: PyTreeSpec,
     unravel_flat: Callable[[torch.Tensor], list[torch.Tensor]],
     flat: torch.Tensor,
+    /,
 ) -> TensorTree:
     return tree_unflatten(treespec, unravel_flat(flat))
 
 
-def _ravel_leaves(
-    leaves: list[torch.Tensor],
-) -> tuple[torch.Tensor, Callable[[torch.Tensor], list[torch.Tensor]]]:
+def _ravel_leaves(leaves: list[torch.Tensor], /) -> tuple[
+    torch.Tensor,
+    Callable[[torch.Tensor], list[torch.Tensor]],
+]:
     if not leaves:
         return (torch.zeros(0), _unravel_empty)
     if not all(torch.is_tensor(leaf) for leaf in leaves):
@@ -155,7 +158,7 @@ def _ravel_leaves(
     )
 
 
-def _unravel_empty(flat: torch.Tensor) -> list[torch.Tensor]:
+def _unravel_empty(flat: torch.Tensor, /) -> list[torch.Tensor]:
     if not torch.is_tensor(flat):
         raise ValueError(f'Expected a tensor to unravel, got {type(flat)!r}.')
     if flat.shape != (0,):
@@ -169,6 +172,7 @@ def _unravel_leaves_single_dtype(
     sizes: tuple[int, ...],
     shapes: tuple[tuple[int, ...], ...],
     flat: torch.Tensor,
+    /,
 ) -> list[torch.Tensor]:
     if not torch.is_tensor(flat):
         raise ValueError(f'Expected a tensor to unravel, got {type(flat)!r}.')
@@ -188,6 +192,7 @@ def _unravel_leaves(
     from_dtypes: tuple[torch.dtype, ...],
     to_dtype: torch.dtype,
     flat: torch.Tensor,
+    /,
 ) -> list[torch.Tensor]:
     if not torch.is_tensor(flat):
         raise ValueError(f'Expected a tensor to unravel, got {type(flat)!r}.')
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 62cc2a61..eb72b344 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -15,7 +15,7 @@
 
 # pylint: disable=missing-function-docstring,invalid-name
 
-import operator
+from operator import itemgetter
 
 import pytest
 
@@ -32,7 +32,7 @@ def test_total_order_sorted():
     assert total_order_sorted([1, 5, 4.5, '20', '3']) == [4.5, 1, 5, '20', '3']
     assert total_order_sorted(
         {1: 1, 5: 2, 4.5: 3, '20': 4, '3': 5}.items(),
-        key=operator.itemgetter(0),
+        key=itemgetter(0),
     ) == [(4.5, 3), (1, 1), (5, 2), ('20', 4), ('3', 5)]
 
     class NonSortable: