'Initializes a urllib3 PoolManager.
This method should not be called from user code, and is only
exposed for use when subclassing the
:class:`HTTPAdapter <requests.adapters.HTTPAdapter>`.
:param connections: The number of urllib3 connection pools to cache.
:param maxsize: The maximum number of connections to save in the pool.
:param block: Block when no free connections are available.
:param pool_kwargs: Extra keyword arguments used to initialize the Pool Manager.'

def init_poolmanager(self, connections, maxsize, block=DEFAULT_POOLBLOCK, **pool_kwargs):

    self._pool_connections = connections
    self._pool_maxsize = maxsize
    self._pool_block = block
    self.poolmanager = PoolManager(num_pools=connections, maxsize=maxsize, block=block, strict=True, **pool_kwargs)
