Python question

Question

def f(x=[]):
x += [3]
return sum(x)
print(f()+f()+f())

Can anyone explain why this code return value 18
I thought each time I will get fresh parameter

Answer 1

It is a bit strange, but what obviously happens is that in each call to f () [3] is added to the existing x

put some print () to check what happens inside the function, or call f () in separate prints

Answer 2

I think what's happening here is the print function is printing the return from f() added to itself three times as a mathematical operator. It prints something like 3 + (3+3) + (3+3+3) which adds up to 18.
If you want to print the numbers individually three times, you could convert them into a list or individual strings, or just use three separate print calls.