pythonarrayslistfunctionset

Can someone explain why this function returns None?


I've been trying to figure out why this function is returning None every time I run it, I would appreciate a lot if someone could explain my why.

x = set([1,2,3])

def inserta(multiconjunto, elemento):
   
   a = multiconjunto.add(elemento)
   
   return a

mc1 = inserta(x, 2)
print(mc1)


Solution

  • It returns none because set.add() returns None, the add() method modifies the set, it does not return a new set.

    There's no reason to put such a simple operation inside your own function, but if you insist you could do this:

    x = set([1,2,3])
    
    def inserta(multiconjunto, elemento):
       multiconjunto.add(elemento)
    
    inserta(x, 2)
    print(x)
    

    if you want to return a new set for some reason then:

    x = set([1, 2, 3])
    
    
    def inserta(multiconjunto, elemento):
        new_set = set(multiconjunto)
        new_set.add(elemento)
    
        return new_set
    
    
    mc1 = inserta(x, 5)
    print(mc1)
    print(x)
    

    should do the trick. It outputs

    {1, 2, 3, 5}
    {1, 2, 3}