Why is the raising of an exception a side effect?

Question

According to the wikipedia entry for side effect, raising an exception constitutes a side effect. Consider this simple python function:

def foo(arg):
    if          


        

Answer 1

From the first line:

"In computer science, a function or expression is said to have a side effect if, in addition to returning a value, it also modifies some state or has an observable interaction with calling functions or the outside world"

The state it modifies is the termination of the program. To answer your other question about why it is not a pure function. The function is not pure because throwing an exception terminates the program therefore it has a side effect (your program ends).