Undefined Behaviour in Python

Question

In C or C++  there is something called undefined behavior.

In expression evaluation when some of the expressions have side-effects, for example, I want to calculate the following:

c = 10
f() + g() + c

but at some point, g makes c = 5

What would be the behavior in python? Would it be undefined as C?

Answer 1

Python evaluates expressions from left to right. Notice that while evaluating an assignment, the right-hand side is evaluated before the left-hand side.

In the following lines, expressions will be evaluated in the arithmetic order of their suffixes:

expr1, expr2, expr3, expr4
(expr1, expr2, expr3, expr4)
{expr1: expr2, expr3: expr4}
expr1 + expr2 * (expr3 - expr4)   <----- This is of importance to us.
expr1(expr2, expr3, *expr4, **expr5)
expr3, expr4 = expr1, expr2