**Behavioral Changes**
- ``Connection: keep-alive`` header is now sent automatically.
-- Read timeout errors will no longer be retried when you create a Session with
- ``max_retries`` greater than zero.
**Improvements**
:param pool_connections: The number of urllib3 connection pools to cache.
:param pool_maxsize: The maximum number of connections to save in the pool.
:param int max_retries: The maximum number of retries each connection
- should attempt. Note, this applies only to failed connections and
- timeouts, never to requests where the server returns a response.
+ should attempt. Note, this applies only to failed DNS lookups, socket
+ connections and connection timeouts, never to requests where data has
+ made it to the server. By default, Requests does not retry failed
+ connections.
:param pool_block: Whether the connection pool should block for connections.
Usage::