[Tutor] Need info regd Singleton class implementation
hi,I need to implement a singleton class in python.Please give me some refernce sites which can help me with the same.Also i want to know to call a destructor for a singleton class.ThanksAkanksha __Do You Yahoo!?Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Need info regd Singleton class implementation
On 6/15/06, Akanksha Govil [EMAIL PROTECTED] wrote: hi, I need to implement a singleton class in python. Please give me some refernce sites which can help me with the same. The online Python Cookbook is a good reference site. Here's the result from a search: http://aspn.activestate.com/ASPN/search?query=singletonx=0y=0section=PYTHONCKBKtype=Subsection I use the following from the printed edition of the Python Cookbook: class Singleton(object): From the 2nd edition of the Python cookbook. Ensures that only one instance is created per running script def __new__(cls, *args, **kwargs): if '_inst' not in vars(cls): cls._inst = object.__new__(cls, *args, **kwargs) return cls._inst André Also i want to know to call a destructor for a singleton class. Thanks Akanksha __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Need info regd Singleton class implementation
Akanksha Govil wrote: I need to implement a singleton class in python. Please give me some refernce sites which can help me with the same. Singletons are not used that much in Python, perhaps because the general culture of we're all adults here is biased against enforcing usage patterns. If you want to have a master reference to an object you can just make it a module attribute. Then any client that needs access to the object just imports the module. Why do you need a singleton? Is this homework? Also i want to know to call a destructor for a singleton class. In Python, destructors (__del__() methods) are called on an object when it is garbage-collected. The details of when this happens vary between different Python implementations. In CPython (the standard Python from python.org), an object is garbage-collected when its reference count goes to 0 - when there are no names that refer to the object. So if you want the __del__() method of an object to be called, you have to ensure that there are no references to the object. In the case of a singleton, this would mean deleting or assigning None to the name that holds the master reference, and ensuring that no users of the singleton retain references to it. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Question about network server in python
Hi there, I am wondering if somebody to could answer a question about sockets. I have a socket that is listening, and a client program connects to it. The client program transfers a name over, and then disconnects from the socket. Now, how that is done is using a socket.close() call to shut down the entire socket. My question is: Is there a way to have the socket close the connection, yet stay open for the next client that comes along and connects to the server? I have my already written code below for further documentation. Thanks! while 1: s=socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1) s.bind((self.ipAddr,self.port)) s.listen(5) print The port is: , self.port client,addr=s.accept() while 1: try: if addr[0] == self.remoteIpAddr: client.send(Connected to the server\n) msg=client.recv(1024) msg=msg.strip() if msg in 'exit': s.close() #Is there a different way to write this? time.sleep(30) print exiting break if len(msg) 0: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about network server in python
I think the problem here is the 'break' statement. Does it not put you outside the while loop whereas in order to keep the server socket open you need it to loop forever. I also think that the s.accept should be inside the while loop. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about network server in python
import socket host = '' port = 57000 s=socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1) s.bind((host,port)) s.listen(5) while 1: client,addr=s.accept() client.send(Connected to the server\n) #if someCondition: # cliente.close() ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about network server in python
Peter Jessop wrote: I think the problem here is the 'break' statement. Does it not put you outside the while loop whereas in order to keep the server socket open you need it to loop forever. I also think that the s.accept should be inside the while loop. There are two loops, I think you missed the outer loop. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Question about network server in python
Tino Dai wrote: Hi there, I am wondering if somebody to could answer a question about sockets. I have a socket that is listening, and a client program connects to it. The client program transfers a name over, and then disconnects from the socket. Now, how that is done is using a socket.close() call to shut down the entire socket. My question is: Is there a way to have the socket close the connection, yet stay open for the next client that comes along and connects to the server? I have my already written code below for further documentation. Thanks! while 1: s=socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1) s.bind((self.ipAddr,self.port)) s.listen(5) print The port is: , self.port client,addr=s.accept() while 1: try: if addr[0] == self.remoteIpAddr: client.send(Connected to the server\n) msg=client.recv(1024) msg=msg.strip() if msg in 'exit': s.close() #Is there a different way to write this? I think you want to close the client socket - client.close() - rather than the master socket. You might be interested in the SocketServer library which helps to write simple socket servers such as this. One advantage of using SocketServer is it makes it trivial to convert your server to a threaded or forked server. Here are some examples: http://www.amk.ca/python/simple/fingerd.py.html http://examples.oreilly.com/pythonian/ see example 19-5 Kent time.sleep(30) print exiting break if len(msg) 0: ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] WinXP IDLE - open file : how-to change default directory ?
Hello,On WinXP IDLE will always 'open' in Python24 folder at startup.A beginner friend of mine hate that (personally I use SPE) and I tried 'quickly' to find a way to configure that for him.I found all the .cfg files in idlelib and also the .idlerc folder in the Documents and settings but I don't see how to give IDLE a default directory at startup (or kipping in memory the last one opened). How to do that or is it just not possible ?Thanks learner404 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] WinXP IDLE - open file : how-to change default directory ?
On 15/06/06, Matthew Webber [EMAIL PROTECTED] wrote: Try right-clicking on the shortcut, select properties, and change the startin value.MatthewScary, I didn't know that windows had that ...Thanks very much Matthew ! P.S. When posting to the list, please use plain text format. From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] OnBehalf Of learner404Sent: 15 June 2006 20:09 To: tutor@python.orgSubject: [Tutor] WinXP IDLE - open file : how-to change defaultdirectory ?Hello,On WinXP IDLE will always 'open' in Python24 folder at startup. A beginner friend of mine hate that (personally I use SPE) and Itried 'quickly' to find a way to configure that for him.I found all the .cfg files in idlelib and also the .idlerc folder in the Documents and settings but I don't see how to give IDLE a defaultdirectory at startup (or kipping in memory the last one opened).How to do that or is it just not possible ?Thanks learner404 ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] XML: Expletive Deleted (OT)
Just picked this up after being out for most of the week... Carroll, Barry [EMAIL PROTECTED] wrote in message One reason to for choosing a human-readable format is the desire to visually confirm the correctness of the stored data and format. Thats a very dangerous asumption, how do you detect unprintable characters, tabs instead of spaces, trailing spaces on a line etc etc. Whole text representations are helpful you should never rely on the human eye to validate a data file. can be invaluable when troubleshooting a bug involving stored data. If there is a tool between the user and the data, one must then rely upon the correctness of the tool to determine the correctness of the data. Or the correctness of the eye. I know which one i prefer - a tested tool. The human eye is not a dta parser, but it flatters to deceive by being nearly good enough. In a case like this, nothing beats the evidence of one's eyes, IMHO. Almost anything beats the human eye IME :-) Actually if you must use eyes do so on a hex dump of the file, that is usually reliable enough if you can read hex... In their book, The Pragmatic Programmer: From Journeyman to Master (Addison Wesley Professional), Andrew Hunt and David Thomas give another reason for storing data in human readable form: The problem with most binary formats is that the context necessary to understand the data is separate from the data itself. You are artificially divorcing the data from its meaning. The data may as well be encrypted; it is absolutely meaningless without the application logic to parse it. With plain text, however, you can achieve a self-describing data stream that is independent of the application that created it. But at a very high risk. I do not dislike text files BTW and am not suggesting that text should not be used but its parsing is best left to machines, the eye is only a rough and unreliable guide. And if your data volumes are high go with binary, you'll need tools to parse a lot of data anyway, you might as well save the space! The Hunt/Thomas book is excellent BTW - I recommend it highly. Even though I disagree witrh several of their suggestions(*) I agree with far more. (*)They recommend sticking with one text editor whereas I use about 5 or 6 on a regular basis depending on the job I'm doing and the platform I'm working on. Emacs on X Windows for new files but vim for quick fix ups, vim on Windows for most things, ed or ex for text based email or over a phone line. This is an example of the resource balancing act that computer people have been faced with since the beginning. The most scarce/expensive resource dictates the program's/system's design. In Alan's example high speed bandwidth is the limiting resource. A data transmission method that fails to minimize use of that resource is therefore a bad solution. Unfortunately the software industry is full of people who by and large don't understand networks so they just ignoire them. At least thats my experience! SOA using SOAP/XML is probably the most inefficient and unreliable set of data networking technologies you could possible come up with. But the focus is on cutting developer cost because the people inventing it are developers! In almost every sizewable project the cost of development will be significantly less than the cost of deployment - in most of my projects it usually works out something like: development - 15% deployment - 30% support - 15% training - 25% documentation - 5% management overhead - 10% Saving 25% of development costs rediuced total cost by around 4% but if that puts deployment costs up by 10% the net gain is only 1%! And in XML case it often puts deployment costs up by 100% - a net loss of 24%!! Now those figures come from a typical project that I work on which probably has a total budget of betwen $10-100 million. If your budget is smaller, say less than $1 million then the balance may well change. But over 50% of the IT industry works on projects with $1m budgets according to both Datamation and Infoweek. [ The only SOA/XML book that addresses this side of XML usage is the excellent SOA - A Field Guide by Peter Erls. Erls also suggests some mitigating strategies to get round it.] So here's my off-topic question: Ajax is being touted as the 'best-known method' (BKM) for making dynamic browser-based applications, and XML is the BKM for transferring data in Ajax land. If XML is a bad idea for network data-transfer, what medium should be used instead? The example I gave of having to upgrade the sites network was actually an early adopter of XML/Ajax architecture! There are lots of other data formats around - some are even self describing (CSV and TLV are cases) Others simply hold the definition in an accessible library so you only have to transport it once - eg IDL and ASN.1 - or optionally compile it into your code for maximum efficiency. ASN./1 is typically around 50
[Tutor] lambda and creating GUIs
I have been reading though the PyGTK tutorial. Can anyone explain how lambda is being used in this statement: button.connect(clicked, lambda w: gtk.main_quit()) This code might put the statement in context: # Create Quit button 66 button = gtk.Button(Quit) 67 68 # When the button is clicked, we call the main_quit function 69 # and the program exits 70 button.connect(clicked, lambda w: gtk.main_quit()) 71 72 # Insert the quit button into the both lower quadrants of the table 73 table.attach(button, 0, 2, 1, 2) 74 75 button.show() The complete script is located at http://www.pygtk.org/pygtk2tutorial/sec-TablePackingExample.html. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] lambda and creating GUIs
(resending to include Tutor -- sorry for the dupe, Christopher) On 16/06/06, Christopher Spears [EMAIL PROTECTED] wrote: I have been reading though the PyGTK tutorial. Can anyone explain how lambda is being used in this statement: button.connect(clicked, lambda w: gtk.main_quit()) Do you understand what lambda does in general? Does it help if I rewrite the code like this: def onQuit(w): gtk.main_quit() button.connect(clicked, onQuit) ? Provided you get your indentation correct (def onQuit and button.connect should be at the same level), and provided you aren't using the name onQuit somewhere else in that method, this code should be a dropin replacement for the line you quote. -- John. ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
