On Sat, 29 Jan 2011 09:03:28 -0500, Roy Smith wrote: > In article <8qijsgfgu...@mid.dfncis.de>, > Frank Dierkes <frank.dier...@googlemail.com> wrote: > >> Naming the first parameter self is only a convention. It could be any >> other name, too. > > But it shouldn't. The use of "self" is so universal that using anything > else will just make your code more difficult for other people to > understand.
It's a strong convention, true, but for Python to prohibit names other than self would be a serious mistake. It would add complication to the parser, for no real benefit. Remember, there's nothing special about methods. They're just ordinary functions which happen to be passed an extra argument at runtime. Making it compulsory to call the first argument "self" would seriously cripple Python's usefulness in at least three cases. (1) Class methods receive the class, not the instance, and the convention is to call that first argument "cls". It would be confusing and misleading to call it "self". Similarly, I sometimes use a similar descriptor which combines the functionality of class methods and ordinary methods. Since neither "self" nor "cls" would be appropriate, I use the name "this" for the first argument: http://code.activestate.com/recipes/577030-dualmethod-descriptor/ Descriptors are a general protocol, so there may be other such technologies being used by people. (2) Sometimes people use functions inside a class namespace as an ordinary function, perhaps as a factory function, called at class creation time. Here is a toy example that automates the building of properties: class K(object): def build(name): # called at class creation time def getter(self): return getattr(self, "_" + name) def setter(self, value): setattr(self, "_" + name, value) return property(getter, setter) spam = build("spam") ham = build("ham") (3) Because methods are just a wrapper around an ordinary function, you can inject almost any function into a class at runtime. You don't know what the first argument of that function is called: >>> class K(object): ... def __init__(self, value='spam'): ... self.attr = value ... >>> def get_attr(obj): ... return obj.attr ... >>> k = K() >>> get_attr(k) 'spam' >>> >>> K.method = get_attr >>> k.method() 'spam' -- Steven -- http://mail.python.org/mailman/listinfo/python-list
