From e8acf0dd4660268d6e30b96829f6eaf22191d428 Mon Sep 17 00:00:00 2001
From: Jiayi Weng <trinkle23897@gmail.com>
Date: Fri, 3 Feb 2023 14:40:05 -0800
Subject: [PATCH] Fix readthedocs build failure (#803)

---
 tianshou/env/utils.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tianshou/env/utils.py b/tianshou/env/utils.py
index ac67101..cbd36d9 100644
--- a/tianshou/env/utils.py
+++ b/tianshou/env/utils.py
@@ -4,7 +4,10 @@ import cloudpickle
 import gymnasium
 import numpy as np
 
-from tianshou.env.pettingzoo_env import PettingZooEnv
+try:
+    from tianshou.env.pettingzoo_env import PettingZooEnv
+except ImportError:
+    PettingZooEnv = None  # type: ignore
 
 if TYPE_CHECKING:
     import gym