Explain this code to me : Explain this code to me. This is a program to print integer inputs as outputs in letters. if i input 35 then output will be thirty five. i understood most of it but want to know how **tens** take the value from 
"twenty thirty forty fifty sixty seventy eighty ninety"

The code is:

    num = int(input("Enter the number:"))
    numbers = ("zero one two three four five six seven eight nine".split())
    numbers.extend("ten eleven twelve thirteen fourteen fifteen sixteen".split())
    numbers.extend("seventeen eighteen nineteen".split())
    numbers.extend(tens if ones == "zero" else (tens + " " + ones) 
        for tens in "twenty thirty forty fifty sixty seventy eighty ninety".split()
        for ones in numbers[0:10])

    print(numbers[num])