[Python] Fix object serialization for multipart requests (#18140)

* Fix multipart object serialization

* Update samples

Author: Poolmann

modules/openapi-generator/src/main/resources/python/rest.mustache

@@ -192,6 +192,8 @@ class RESTClientObject:
                     # Content-Type which generated by urllib3 will be
                     # overwritten.
                     del headers['Content-Type']
+                    # Ensures that dict objects are serialized
+                    post_params = [(a, json.dumps(b)) if isinstance(b, dict) else (a,b) for a, b in post_params]
                     r = self.pool_manager.request(
                         method,
                         url,

samples/client/echo_api/python-disallowAdditionalPropertiesIfNotPresent/openapi_client/rest.py

@@ -203,6 +203,8 @@ def request(
                     # Content-Type which generated by urllib3 will be
                     # overwritten.
                     del headers['Content-Type']
+                    # Ensures that dict objects are serialized
+                    post_params = [(a, json.dumps(b)) if isinstance(b, dict) else (a,b) for a, b in post_params]
                     r = self.pool_manager.request(
                         method,
                         url,

samples/client/echo_api/python/openapi_client/rest.py

@@ -203,6 +203,8 @@ def request(
                     # Content-Type which generated by urllib3 will be
                     # overwritten.
                     del headers['Content-Type']
+                    # Ensures that dict objects are serialized
+                    post_params = [(a, json.dumps(b)) if isinstance(b, dict) else (a,b) for a, b in post_params]
                     r = self.pool_manager.request(
                         method,
                         url,

samples/openapi3/client/petstore/python/petstore_api/rest.py

@@ -202,6 +202,8 @@ def request(
                     # Content-Type which generated by urllib3 will be
                     # overwritten.
                     del headers['Content-Type']
+                    # Ensures that dict objects are serialized
+                    post_params = [(a, json.dumps(b)) if isinstance(b, dict) else (a,b) for a, b in post_params]
                     r = self.pool_manager.request(
                         method,
                         url,