[Tutor] creating read only attributes

[Daniel Ehrenberg]

--- Thomi Richards wrote:
> Hi guys,
> 
> 
> I've been looking at some Delphi recently, and you
> can create read only 
> attributes, which behave like variables. consider
> the following code:
> 
> type TTest = class
> 	private
> 		testvar = integer;
> 	public
> 		property Test: integer read testvar;
> 		constructor Create;
> 	end;
> 
> 
> Now, while I *hate* Delphi code with a vengeance,
> this is pretty cool; I can 
> not do something like this:
> 
> t := TTest.Create;
> writeln(t.Test);
> 
> i.e.- the "Test" property looks and behaves exactly
> like a normal variable, 
> except that it is read-only in this case.
> 
> The property can even be the result of a function,
> like so:
> 
> 
> type TTest = class
> 	private
> 		function test: integer;
> 	public
> 		property Test: integer read test;
> 		constructor Create;
> 	end;
> 
> And it is still used like 'Test" as a normal
> variable. This has the obvious 
> advantage of being able to change the code within a
> class, without having to 
> change external code which implements these
> features. (does that make sense)?
> 
> I'm sure there's a way to do this in python, but I
> haven't found it yet.
> 
> A common usage I've seen is having method names like
> "set_text" and 
> "get_text", but these still behave like functions.
> You cannot do something 
> like this:
> 
> t.set_text = 123.456
> 
> well, you could, but it wouldn't do what you
> expected....
> 
> Can someone please point me in the right direction?
> what's the magic keyword 
> I'm missing?
> 
> 
> Thanks in advance ;)
> 
> - -- 
> Thomi Richards,
> http://once.sourceforge.net/

There is no native thing to do this, but it can
probably be done using __setattr__, but I can't do it
without getting an infinite recursion. However, I
don't see why you really need to do this. It is a
convention to not change things that are in allcaps,
so if someone wants to write a working application,
they probably won't do that. In general, creating
private variables is considered unpythonic, so it is
probably the same for these immutable variables.
Daniel Ehrenberg

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