From dbbdae4aa5d051b1a3a492936c9556bcfcfae490 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Robert?= <cr52@protonmail.com>
Date: Fri, 26 Nov 2021 17:59:31 +0100
Subject: [PATCH] TYP: add type annotation

---
 yt/utilities/on_demand_imports.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/yt/utilities/on_demand_imports.py b/yt/utilities/on_demand_imports.py
index a56ec7afa1d..fc7bf6bcab6 100644
--- a/yt/utilities/on_demand_imports.py
+++ b/yt/utilities/on_demand_imports.py
@@ -1,6 +1,7 @@
 import sys
 from importlib import import_module
-from typing import Optional
+from types import ModuleType
+from typing import Dict, Optional, Union
 
 if sys.version_info >= (3, 8):
     from functools import cached_property
@@ -36,7 +37,7 @@ class OnDemandImport:
 
     def __init__(self, name: str, instructions: Optional[str] = None):
         self._name = name
-        self._submodules = {}
+        self._submodules: Dict[str, Union[ModuleType, "OnDemandImport"]] = {}
         msg = f"Failed to import an optional dependency from yt ({self._name})."
         if instructions:
             msg += f"\n{instructions}"