From 7ebb75c7ff1fd28e7d17536a39b62616a8705821 Mon Sep 17 00:00:00 2001
From: PrettyWood <em.jolibois@gmail.com>
Date: Wed, 29 Jul 2020 09:17:02 +0200
Subject: [PATCH] chore: improve `safe_issubclass`

---
 pydantic/schema.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/pydantic/schema.py b/pydantic/schema.py
index 80e5dc7396d..fb98af898d1 100644
--- a/pydantic/schema.py
+++ b/pydantic/schema.py
@@ -638,8 +638,11 @@ def field_singleton_sub_fields_schema(
 
 
 def safe_issubclass(a: Any, b: Any) -> bool:
-    # `typing.Pattern` is not a valid type
-    return issubclass(a, b) if a is not Pattern else (a is b)
+    """If `a` is not a valid class (e.g. `typing.Pattern`), `issubclass` works only if `a is b`"""
+    try:
+        return issubclass(a, b)
+    except TypeError:
+        return False
 
 
 def add_field_type_to_schema(field_type: Any, schema: Dict[str, Any]) -> None: