tcp_server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

What is socket.AF_INET and socket.SOCK_DGRAM? What do they do?

AF_INET, where AF represents address family, is used to specifiy the type of address family with which the socket can communicate. To be specific, it is used for Internet Protocol v4 addresses (IPV4) with the value set to be 2.

Other address family members include:

  Name                   Purpose                 
   AF_UNIX, AF_LOCAL      Local communication              
   AF_INET                IPv4 Internet protocols        
   AF_INET6               IPv6 Internet protocols
   AF_IPX                 IPX - Novell protocols
   AF_NETLINK             Kernel user interface
 
 device    
   AF_X25                 ITU-T X.25 / ISO-8208 protocol 
   AF_AX25                Amateur radio AX.25 protocol
   AF_ATMPVC              Access to raw ATM PVCs
   AF_APPLETALK           Appletalk                      
   AF_PACKET              Low level packet interface   

As for socket.SOCK_DGRAM, where DGRAM stands for datagram, it is used to specify the type of connection to be created. In this case, it is a constant of value 2 representing UPD connection.