diff --git a/modules/openapi-generator/src/main/resources/python/api_client.mustache b/modules/openapi-generator/src/main/resources/python/api_client.mustache
index b89911d51d2..b0976ba9f2b 100644
--- a/modules/openapi-generator/src/main/resources/python/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/python/api_client.mustache
@@ -58,7 +58,7 @@ class ApiClient(object):
     _pool = None
 
     def __init__(self, configuration=None, header_name=None, header_value=None,
-                 cookie=None, pool_threads=None):
+                 cookie=None, pool_threads=1):
         if configuration is None:
             configuration = Configuration()
         self.configuration = configuration
diff --git a/samples/client/petstore/python-asyncio/.openapi-generator/VERSION b/samples/client/petstore/python-asyncio/.openapi-generator/VERSION
index e24c1f857e0..afa63656064 100644
--- a/samples/client/petstore/python-asyncio/.openapi-generator/VERSION
+++ b/samples/client/petstore/python-asyncio/.openapi-generator/VERSION
@@ -1 +1 @@
-3.3.3-SNAPSHOT
\ No newline at end of file
+4.0.0-SNAPSHOT
\ No newline at end of file
diff --git a/samples/client/petstore/python-tornado/.openapi-generator/VERSION b/samples/client/petstore/python-tornado/.openapi-generator/VERSION
index e24c1f857e0..afa63656064 100644
--- a/samples/client/petstore/python-tornado/.openapi-generator/VERSION
+++ b/samples/client/petstore/python-tornado/.openapi-generator/VERSION
@@ -1 +1 @@
-3.3.3-SNAPSHOT
\ No newline at end of file
+4.0.0-SNAPSHOT
\ No newline at end of file
diff --git a/samples/client/petstore/python/.openapi-generator/VERSION b/samples/client/petstore/python/.openapi-generator/VERSION
index e24c1f857e0..afa63656064 100644
--- a/samples/client/petstore/python/.openapi-generator/VERSION
+++ b/samples/client/petstore/python/.openapi-generator/VERSION
@@ -1 +1 @@
-3.3.3-SNAPSHOT
\ No newline at end of file
+4.0.0-SNAPSHOT
\ No newline at end of file