use hasattr instead of getattr with test

Author: jima80525

concurrency-overview/io_threading.py

@@ -9,7 +9,7 @@
 
 
 def get_session():
-    if not getattr(thread_local, "session", None):
+    if not hasattr(thread_local, "session"):
         thread_local.session = requests.Session()
     return thread_local.session