Snipplr

(Python) Formatting date strings in Python - chombee

Thu, 15 Jan 2009 14:15:02 UTC

[date](http://docs.python.org/library/datetime.html#datetime.date), [datetime](http://docs.python.org/library/datetime.html#datetime.datetime) and [time](http://docs.python.org/library/datetime.html#datetime.time) objects in Python have a [strftime](http://docs.python.org/library/datetime.html#strftime-behavior) method for creating string representations in whatever format you want. (See the strftime link for the strftime syntax.)

(Python) Import a file from a directory - chombee

Thu, 15 Jan 2009 13:50:14 UTC

When you want to import a python file but that file is not in the same directory as the python file you're importing _from_ (e.g. it's in a subdir). You need to add the directory that contains the file you want to import to your path environment variable `sys.path`. `sys.path` contains all the places python will look for a file when you do an import.

(Python) Creating and removing files and dirs with Python OS module - chombee

Tue, 15 Jul 2008 20:44:02 UTC

Effbot's page on the os module: http://effbot.org/librarybook/os.htm The os module has lots of methods for dealing with files and directories: http://docs.python.org/lib/os-file-dir.html The shutil module: http://docs.python.org/lib/module-shutil.html

(Python) Listing directories in Python - chombee

Wed, 09 Jul 2008 13:57:08 UTC

(Python) Unit tests with Python - chombee

Mon, 16 Jun 2008 10:35:25 UTC

Test-first programming, in which you write the unit tests first with the unittest module and then work on the code until it passes all the tests, seems like a good substitute for writing interfaces or documentation first. The unit tests are like an API, describing the interface of the code being tested. And they lend themselves well to refactoring. This is a first attempt at a unit test for the messager.py module posted earlier.

(Python) Messager pattern from Panda3D - chombee

Wed, 11 Jun 2008 07:03:17 UTC

This is my implementation of the messager pattern used by Panda3D for event handling. It's a really nice idea but I think Panda's version is implemented weirdly, it uses the subscribe objects as keys in the dictionary. That means that if you want more than one object to subscribe to the same message you _have_ to subclass DirectObject and use self.accept(...), can't just call the messager directly or you'll get a different behaviour, it means that a single object instance can't subscribe two different functions to the same message, and it means that your _objects_ have to be _hashable_ (!) because the messager uses them as keys in a dictionary. It seems to me that it would be much simpler if the messager's dictionary just mapped message names to function objects, so that's what I did. Use this pattern when you have a lot of objects spread throughout the class hierarchy that need to communicate with each other. It's a way of implementing one-to-many or many-to-many communication, in which an object can send a message to many receivers without needing to know who those receivers are, or how many receivers there are, or even if there are any receivers (although an object can potentially check all these things if it wants to). The singleton messager object receives messages from broadcaster objects and forwards them to receiver objects. Setup a single, simple, generic, system- wide messaging system, instead of creating different systems for each different type of message or messaging relation. The disadvantage of just implementing this pattern once and using it everywhere is that with lots of senders and receivers it might become difficult to understand and debug message-based behaviour. Particularly if the order in which messages are sent and received becomes important, when you send a message with this pattern there's no way of knowing in what order the receiver objects will receive the message, and therefore know way of knowing in what order their responses will be executed, and those responses may include sending more messages. You can implement some ordering relations by having an object receive a message, deal with it, then send a different message to other recievers, but I wouldn't want to overuse that. Also you have to be careful to avoid clashes in message names. The GoF Mediator and Observer patterns are similar in that they enable a mode of communication between objects in which the sender object broadcasts a message without needing to know all of the receiver objects, and the receiver objects can receive messages without being tightly coupled to the sender object(s). In the GoF Mediator pattern, the Mediator object is more than just a messager that passes messages between other objects and leaves the behaviour up to the others. The mediator actually encapsulates the interaction behaviour between objects, deciding which methods to call on which objects each time it receives a notification from an object. Mediator centralises control of how objects cooperate in the mediator class, whereas the Messager pattern leaves this control distributed throughout the objects themselves. In the GoF observer pattern a one-to-many dependency is setup, there is no separate Messager object but rather the sender object itself maintains the list of reciever object and notifies them of new messages. With its separate messager object the Messager pattern enables many-to-many dependencies as well as one-to-many.

(Python) Reading and writing text files in Python - chombee

Mon, 09 Jun 2008 09:48:40 UTC

(Python) Creating list-like objects in Python - chombee

Sun, 08 Jun 2008 18:34:00 UTC

(Python) Creating dictionary-like objects in Python using DictMixin - chombee

Mon, 02 Jun 2008 11:45:35 UTC

(Python) Adding and removing collide masks - chombee

Fri, 30 May 2008 12:20:55 UTC

(Python) Panda3D's BitMask32 class (collision masks) - chombee

Fri, 30 May 2008 11:35:29 UTC