Using a while loop to compute the sum of integers from two numbers

Question

I'm having some trouble with a homework problem on MyPytutor which is asking me to write a function sum_from_to(start, end) that uses a while loop to compute the sum of the integers from start up to, but not including end.

The given code is:

def sum_from_to(start, end):
"""Return the sum of the integers from start up to but not including end.

sum_from_to(int, int) -> int
"""
# add your code here: use a while loop

Examples:

• sum_from_to(3, 7) should evaluate to 18 (ie 3+4+5+6).
• sum_from_to(3, 3) should evaluate to 0.

How would I approach this? I've seen this same question from half a year ago but it was never resolved. Any help would be greatly appreciated as I'm really stuck on this!

Answer 1

Initialize a while loop between [start, end[ (with end excluded with this sign : "<") Then iterate on the start number. So for 3 to 7 the numbers will be : 3,4,5,6 Then you just have to add this numbers, so just initialize a var befor your while loop and add this var with the number you iterate

def sum_from_to(start, end):
    """Return the sum of the integers from start up to but not including end.

    sum_from_to(int, int) -> int
    """
    result = 0
    i = start
    while i < end:
        result += i
        i += 1
    return result

Answer 2

Here are some examples to get you started

a = 0
while a < 10:
    a += 1
    print a

You could probably do it with

sum(range(start, end))

Answer 3

I'd delivery this:

def sum_from_to(start, end):
    ret = 0
    while start < end:
        ret += start
        start += 1
    return ret

But I like the way it looks below (without the while - which doesn't fit your requirements):

def sum_from_to(start, end):
    return sum(x for x in range(start, end))