code: def assert_free(self, host, port=None):
  		
  		if port is None and isinstance(host, abc.Sequence):
  			host, port = host[:2]
  		if platform.system() == 'Windows':
  			host = client_host(host)
  		info = socket.getaddrinfo(
  			host, port, socket.AF_UNSPEC, socket.SOCK_STREAM,
  		)
  		list(itertools.starmap(self._connect, info))
docs: Assert that the given addr is free
  		in that all attempts to connect fail within the timeout
  		or raise a PortNotFree exception.
  
  		>>> free_port = find_available_local_port()
  
  		>>> Checker().assert_free('localhost', free_port)
  		>>> Checker().assert_free('127.0.0.1', free_port)
  		>>> Checker().assert_free('::1', free_port)
  
  		Also accepts an addr tuple
  
  		>>> addr = '::1', free_port, 0, 0
  		>>> Checker().assert_free(addr)
  
  		Host might refer to a server bind address like '::', which
  		should use localhost to perform the check.
  
  		>>> Checker().assert_free('::', free_port)