Fair Battle [Help wanted]

Here is my current code for the level :

# Attack when your soldiers' total health is greater
# than the ogres' total health

# Write a function that takes an array of units as input
# And returns the sum of all the units' health
def sumHealth():
    totalHealth = 0
    unitIndex = 0
    while unitIndex < len():
        currentUnit = 
        totalHealth = totalHealth + currentUnit.health
    return totalHealth

while True:
    friends = hero.findFriends()
    enemies = hero.findEnemies()
    # Get the total health of your soldiers and the ogres.
    # Say "Attack" when your side has more total health.

My problem here is that I don’t know what to put in the function between paranthese for the len(): part. I know how to do the sumHealth functions for a particular array, for example I’d know how to find the totalHealth of the enemies array by itself, but I would need 2 seperate functions to find the totalHealth of each of the arrays, one for each. Could anybody help with explaining how I would go about doing this for finding the totalHealth using only the one function (as I expect is wanted, I think they are wanting you to use one function for both arrays). Also, how would I do the “get the total health of your soldiers and the ogres” part?

Use parameter units for function and for len().

How would I go about defining “units”?
Also, is the last part of my code current (in the picture) for getting the total Health of my soldiers and the ogres? What about the if statement on the 2nd to last line?

def sumHealth(units):



New error now.

Increment unitIndex.