lass:`http.client.HTTPConnection`.

    .. note::
       Only works in Python 2. This parameter is ignored in Python 3.

:param timeout:
    Socket timeout in seconds for each individual connection. This can
    be a float or integer, which sets the timeout for the HTTP request,
    or an instance of :class:`urllib3.util.Timeout` which gives you more
    fine-grained control over request timeouts. After the constructor has
    been parsed, this is always a `urllib3.util.Timeout` object.

:param maxsize:
    Number of connections to save that can be reused. More than 1 is useful
    in multithreaded situations. If ``block`` is set to False, more
    connections will be created but they will not be saved once they've
    been used.

:param block:
    If set to True, no more than ``maxsize`` connections will be used at
    a time. When no free connections are available, the call will block
    until a connection has been released. This is a useful side effect for
    particular multithreaded situations where one does not want to use more
    than maxsize connections per host to prevent flooding.

:param headers:
    Headers to include with all requests, unless other headers are given
    explicitly.

:param retries:
    Retry configuration to use by default with requests in this pool.

:param _proxy:
    Parsed proxy URL, should not be used directly, instead, see
    :class:`urllib3.ProxyManager`

:param _proxy_headers:
    A dictionary with proxy headers, should not be used directly,
    instead, see :class:`urllib3.ProxyManager`

:param \**conn_kw:
    Additional parameters are used to create fresh :class:`urllib3.connection.HTTPConnection`,
    :class:`urllib3.connection.HTTPSConnection` instances.
