How is Python designed?

[Diez B. Roggisch]

> Of course for such simple expression, that function
> will not run recursively, but for more complex
> expressions, it will, as a example:
>  a + b * ( c + ( d - e ) / f )...

No, it won't. You seem to not properly understand what recursion is, and
confuse it with overloaded methods. The compute-method of an expression ast
node is called once for every node - to yield its value. Not more - not
less. The fact for 

a * b

the compute methods of objects representing the variables a and b is called
inside a binary operator object neither makes it recursive nor costs more
time.

So there are three compute calls - first on the *-Operator object, then on a
and b.

Using depth-first-search, there are three calls of compute - first on a, b,
then on *.

So three compute calls in both cases. As I said before: No reason not to do
depth-first, if it suits your needs. But it won't buy you anything.

-- 
Regards,

Diez B. Roggisch