def f(a, b="world", c=0): 
    print (" ".join([a, b, str(c)]))

f("hello")                  # hello world 0
f("hello", "lab")           # hello lab 0
f("hello", "lab", 2)        # hello lab 2
f("hello", c=2)             # hello world 2
f("hello", "lab", c=2)      # hello lab 2