On Oct 30, 1:13 am, Joe Strout <[EMAIL PROTECTED]> wrote: > On Oct 29, 2008, at 4:52 PM, Fuzzyman wrote: > > > You're pretty straightforwardly wrong. In Python the 'value' of a > > variable is not the reference itself. > > That's the misconception that is leading some folks around here into > tangled nots of twisty mislogic, ultimately causing them to make up > new terms for what every other modern language is perfectly happy > calling Call-By-Value. > > I've thought a lot about why this misconception is so widespread here, > and I think it must be one of the following: > > 1. There was one community leader with this idea, who has been > successful at promoting it widely, much to the detriment of all; or, > > 2. Because everything in Python is an object, you're not forced to > think clearly (and more generally) about references as values as you > are in languages (such as Java, VB.NET, etc.) which have both simple > types and object types. >
To make it clearer for you, call by value means that the value is copied in - and therefore changes to the value won't be visible to the caller. In .NET this is true of mutable value types - changes made are made to a copy and not visible to the caller. In Python we *only* have reference types, so changes to *any* mutable object are visible to the caller. In .NET you can call by reference with a value type - and the runtime does boxing for you so that you can see the changes. You have to explicitly ask for call by reference though. Michael > Either way, it's wrong (or at least, a needlessly complicated way of > looking at things). > > > .NET does draw a distinction between 'value types' and reference types > > - where using reference types are called by reference (the reference > > is passed) and value types are called by value (the value itself is > > copied). > > Quite right. Now, note that "ByRef" and "ByVal" apply to both. > Generalize to Python. There you go. > > Best, > - Joe > > P.S. I really am trying to quit responding to this thread. Sometimes > the urge is too strong. But I'll keep trying! -- http://mail.python.org/mailman/listinfo/python-list
