When you iterate a list using for i in lst the i is the value not the index, so in your case, it will be like below example. BTW: I guess you need to learn some basics of python list iteration.
See: https://favtutor.com/blogs/python-iterate-through-list.
Note: I just edited the largest variable using numbers[0] otherwise your program will not able to find the max value when you have negative values in the list.
numbers = [12, 33, 44, 55, 11, 19, 98, 17, 12]
largest = numbers[0] # take first element as max
for value in numbers:
if largest < value:
largest = value
print(largest)
OR with single line python max()
largest = max(numbers)
Working Code: https://rextester.com/CLBM63548
print(max(numbers))?