code: def connection_from_host(self, host, port=80, scheme='http'):
          
          pool_key = (scheme, host, port)
  
          # If the scheme, host, or port doesn't match existing open connections,
          # open a new ConnectionPool.
          pool = self.pools.get(pool_key)
          if pool:
              return pool
  
          # Make a fresh ConnectionPool of the desired type
          pool_cls = pool_classes_by_scheme[scheme]
          pool = pool_cls(host, port, **self.connection_pool_kw)
  
          self.pools[pool_key] = pool
  
          return pool
docs: Get a :class:`ConnectionPool` based on the host, port, and scheme.
  
          Note that an appropriate ``port`` value is required here to normalize
          connection pools in our container most effectively.