Python递归，打印两个整数之间的值

Question

I am wanting to recursively print all integers between two integers given as inputs to the print_numbers function.

So far I have gotten:

def print_numbers(start,stop):
    if start == stop:
        print(start)
    else:
        print(start)
        print(print_numbers(start + 1,stop))

But when calling print_numbers(1,5) I get:

1
2
3
4
5
None
None
None
None

I can't seem to figure out where the none is coming from.

Answer 1

When you are calling print_between , print_between does not return anything and so when you do print(print_between(start + 1,stop)) , it prints None because the function returns None .

Replace

print(print_between(start + 1,stop))

with

print_between(start + 1,stop)

Also, make sure your function name is print_between and not print_numbers

Check out a quick DEMO here

Answer 2

The default return value of a function is None. you don't need to print it.

def print_numbers(start,stop):
    if start == stop:
        print(start)
    else:
        print(start)
        print_between(start + 1,stop)