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CHAPTER 24 ■ PROJECT 5: A VIRTUAL TEA PARTY 465 def __init__(self, server): self.server = server self.sessions = [] def add(self, session): self.sessions.append(session) def remove(self, session): self.sessions.remove(session) def broadcast(self, line): for session in self.sessions: session.push(line) def do_logout(self, session, line): raise EndSession In addition to the basic add and remove methods, a broadcast method simply calls push on all of the users (sessions) in the room. There is also a single command defined—logout (in the form of the do_logout method). It raises an exception (EndSession), which is dealt with at a higher level of the processing (in found_terminator). Login and Logout Rooms In addition to representing normal chat rooms (this project includes only one such chat room), the Room subclasses can represent other states, which was indeed the intention. For example, when a user connects to the server, he or she is put in a dedicated LoginRoom (with no other users in it). The LoginRoom prints a welcome message when the user enters (in the add method). It also overrides the unknown method to tell the user to log in; the only command it responds to is the login command, which checks whether the name is acceptable (not the empty string, and not used by another user already). The LogoutRoom is much simpler. Its only job is to delete the user’s name from the server (which has a dictionary called users where the sessions are stored). If the name isn’t there (because the user never logged in), the resulting KeyError is ignored. For the source code of these two classes, see Listing 24-6 later in this chapter. ■Note Even though the server’s users dictionary keeps references to all the sessions, no session is ever retrieved from it. The users dictionary is used only to keep track of which names are in use. However, instead of using some arbitrary value (such as 1), I decided to let each user name refer to the corresponding session. Even though there is no immediate use for it, it may be useful in some later version of the program (for example, if one user wants to send a message privately to another). An alternative would have been to simply keep a set or list of sessions.
466 CHAPTER 24 ■ PROJECT 5: A VIRTUAL TEA PARTY The Main Chat Room The main chat room also overrides the add and remove methods. In add, it broadcasts a message about the user who is entering, and it adds the user’s name to the users dictionary in the server. The remove method broadcasts a message about the user who is leaving. In addition to these methods, the ChatRoom class implements three commands: • The say command (implemented by do_say) broadcasts a single line, prefixed with the name of the user who spoke. • The look command (implemented by do_look) tells the user which users are currently in the room. • The who command (implemented by do_who) tells the user which users are currently logged in. In this simple server, look and who are equivalent, but if you extend it to contain more than one room, their functionality will differ. For the source code, see Listing 24-6 later in this chapter. The New Server I’ve now described most of the functionality. The main additions to ChatSession and ChatServer are as follows: • ChatSession has a method called enter, which is used to enter a new room. • The ChatSession constructor uses LoginRoom. • The handle_close method uses LogoutRoom. • The ChatServer constructor adds the dictionary users and the ChatRoom called main_room to its attributes. Notice also how handle_accept no longer adds the new ChatSession to a list of sessions because the sessions are now managed by the rooms. ■Note In general, if you simply instantiate an object, like the ChatSession in handle_accept, without binding a name to it or adding it to a container, it will be lost, and may be garbage collected (which means that it will disappear completely). Because all dispatchers are handled (referenced) by asyncore (and async_chat is a subclass of dispatcher), this is not a problem here. The final version of the chat server is shown in Listing 24-6. For your convenience, I’ve listed the available commands in Table 24-1. An example chat session is shown in Figure 24-1— the server in that example was started with the command python chatserver.py
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Beginning Python From Novice to Pro
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Index ■Symbols - operator 558 !=
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