per9000 wrote: > Hi, > > I recently started working a lot more in python than I have done in > the past. And I discovered something that totally removed the pretty > pink clouds of beautifulness that had surrounded my previous python > experiences: magic names (I felt almost as sad as when I discovered > the strange pink worms that eat you in nethack, not to mention the > mind flayers - I really hate them). > > I guess all programming languages have magic names to some extent > (f.x. classes in the "C-family" have constructors that must have the > same name as the class (foo::foo) instead of foo.__init__). > > I just used a search engine a little on this topic and I found no > comprehensive list of magic names in python. > > So my questions: > * is there a comprehensive list of magic names in python (so far i > know of __init__ and __repr__)? > * are these lists complete or can magic names be added over time (to > the python "core")? > * are magic names the same in different python versions? > > I also tried (selected parts of(?)) the unittest package for use in > Zope and it seemed functions that I created for my test with the magic > prefix "test" were magic, other functions were not. > > So another question emerges: > * is the use of magic names encouraged and/or part of good coding > practice. >
What is "magic" about __init__ and __repr__? They are identifiers just like "foo" or "JustAnotherClass". They have no special meaning to the Python compiler. The leading and trailing double underscores represent no special incantation. It is just a naming convention. So a number of method names like __init__ and __repr__ have a pre-defined usage. In every other respect they are just normal methods. They can be called directly. When dir() is called on a class they show up along with other method names. They can appear in a class declaration or added later after the class is created, just like other methods. They differ in that sometimes they will be called implicitly, such as when creating a new object or by the print statement. As to whether to use them: absolutely. __init__ is the preferred way to initialize a new object. Providing a __repr__ or __str__ method lets objects display descriptive and meaningful information about themselves in print statements and exception messages. And various other "special methods" allow for user defined versions of Python's built-in types. In fact most built-in types can be extended by subclassing and overriding their special methods. Back to "magic names". Python is a consistent language. What may be special cased - "magic" - in another language is handled normally with Python's general purpose dynamic type system. In fact I can think of only one name I would call "magic": __future__. from __future__ import <feature> does have special meaning to the Python compiler. It does more than import a module. -- Lenard Lindstrom <[EMAIL PROTECTED]> -- http://mail.python.org/mailman/listinfo/python-list
