[Python] Memory leak in generated client

Description

Memory leak and accumulated slowness when initializing auto-generated python client from any swagger.

Swagger-codegen version

v2.4.10

Swagger declaration file content or url

When creating python client, and initializing it, a memory leak takes place. When doing it a lot of time, the memory goes up to GBs, and initializing another client can take 10s of seconds.

Steps to reproduce

1. Create and download a python client from https://editor.swagger.io/. Use any swagger you want.
2. Create a.py:

import time
import swagger_client.api_client as api
while True:
    before = time.time()
    api.ApiClient()
    print time.time() - before

3. $ python a.py
4. At first it takes ~0.003 seconds per loop on my computer and the memory 51MB:
   
5. After 5 minutes it takes ~0.005 and the memory is up to 170MB
   
6. After a few hours the memory is GBs and the time per loop is a few seconds

Suggest a fix/enhancement

Note the bug doesn't happen in version v3.0.14.