Why such strange behavior of the variable after recursion?

Question

Python

Here everything was fine:

def test(mass):
    print("До рекурсии:",mass)
    
    if mass==1: return
    mass=mass-1
    test(mass)
    
    print("после рекурсии:",mass)
    
    
test(4)

But why is there such a mess?

def test(mass):
    print("До рекурсии:",mass)
    
    if len(mass)==1: return
    del mass[0]
    test(mass)
    
    print("после рекурсии:",mass)
    
    
test([4,3,2,1])

I've been fighting for a few hours now :-(

Answer 1

Because when passing a list as a parameter, it is not the list itself that is copied, but a link to it. When calling recursively, masspass mass.copy().

Answer 2

You pass the same list, elements are removed from it.