On Wed, 14 Dec 2005 18:35:51 +0000, Tom Anderson wrote: > On Wed, 14 Dec 2005, Steven D'Aprano wrote: > >> On Wed, 14 Dec 2005 10:57:05 +0100, Gabriel Zachmann wrote: >> >>> I was wondering why python doesn't contain a way to make things "const"? >>> >>> If it were possible to "declare" variables at the time they are bound >>> to objects that they should not allow modification of the object, then >>> we would have a concept _orthogonal_ to data types themselves and, as a >>> by-product, a way to declare tuples as constant lists. >> >> In an earlier thread, somebody took me to task for saying that Python >> doesn't have variables, but names and objects instead. > > I'd hardly say it was a taking to task - that phrase implies > authoritativeness on my part! :) > >> This is another example of the mental confusion that occurs when you >> think of Python having variables. > > What? What does this have to do with it? The problem here - as Christopher > and Magnus point out - is the conflation in the OP's mind of the idea of a > variable, and of the object referenced by that variable. He could have > expressed the same confusion using your names-values-and-bindings > terminology - just replace 'variable' with 'name'. The expression would be > nonsensical, but it's nonsensical in the variables-objects-and-pointers > terminology too.
If the OP was thinking names-and-bindings, he would have immediately realised there is a difference between unmodifiable OBJECTS and unchangeable NAMES, a distinction which doesn't appear to have even passed his mind. "Variable" is a single entity of name+value, so it makes perfect sense to imagine a variable with a constant, unchangeable value. But a name+object is two entities, and to implement constants you have to have both unmodifiable objects and names that can't be rebound -- and even that may not be sufficient. -- Steven. -- http://mail.python.org/mailman/listinfo/python-list
