Others have provided workarounds I'll attempt to answer the rationale part...
> Why is it that when one variable is assigned a value in terms of another > variable, assigning a new value to the first doesn't change the value of > the > second? Python variables are just names that refer to a value. The value can be any kind of object that python recognises but it is a single value. When you assign an expression to a variable Python evaluates the current value of the expression before assigning it, it does not understand the concept of an expression as a value in its own right. The only way to store an expression is to place it in a function as the others have shown. The function can then be cxalled as needed, but it must be called explicitly, you cannot call it by implication when one of the terms of the expression changes. There is a way to fake this a little using properties of a class. If you create a class that has all your variables as properties, then you can write get/set methods for those properties such that when changed they automatically update the other properties, thus rippling the changes through your system. But using properties like this is a slightly esoteric technique in Python. HTH, Alan G Author of the learn to program web tutor http://www.freenetpages.co.uk/hp/alan.gauld _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
