def print_if(header, indent=0):
    p = print_ifer(header, indent)
    next(p)
    return p.send


def print_ifer(header, indent=0):
    data = (yield)
    print(" " * indent + header)
    indent += 4
    while(True):
        print(" " * indent + str(data))
        data = (yield)


p = print_if("hello", 4)
for i in range(3):
    p(i)