Joining elements in a list without the join command

You could just convert each element to a string, add them, and then convert back to an int:

def lists(list1):
    answer=''
    for number in list1:
        answer+=str(number)
    print(int(answer))


lists([12,4,15,11])

---

>>> 
1241511

If you just want to print the number rather than return an actual int:

>>> a = [12,4,15,11]
>>> print(*a, sep='')
1241511