Adding odd numbers in a list

Question

I am trying to find the sum of all odd numbers within a given range but I cannot figure out how to specify which numbers are odd. My professor said to use \"for num in numbe

Answer 1

Just to make a quick comment in the form of an answer. If you wanted to make a list of all the odd number in a between 0 and 10, the end points don't matter. If the list was from 0 to 11 then the end point matters. Just remember that range(0,11) = [0,1,2,3,4,5,6,7,8,9,10] and won't include 11.

---

Now to explain the generator that is being used. To make to list using numbers as defined by you, you could do this.

odds = []
for num in numbers:
    if num % 2 == 1:
        odds.append(num)

This would give you odds = [1,3,5,7,9]. Python has something call list comprehension that make it really easy to do things like this. The above can be easily written like this

odds = [num for num in number if num % 2 == 1]

and since you want the sum off all the numbers in the list and the sum function takes list, the answer is just

sum([num for num in number if num % 2 == 1])

Note that most of the answer don't have brackets. This is because without it it becomes a generator.

odds = (num for num in number if num % 2 == )
print odds  #-->  at 0x7f9d220669b0>
odds.next() # 1
odds.next() # 3
...

Since sum takes these as well and generator are faster and less memory intensive than list that is why the best answer is

sum(num for num in numbers if num % 2 == 1)