Assuming you just need the largest number, removing the unwanted code. You do not need the nested loop here. Update your function to:
def largest_num(values,n,b):
a = 0;
start = 0;
for i in range(n - 1):
if(values[i+1] > values[i]:
largest = values[i+1]
else:
largest = values[i]
print(largest)
You may achieve the same using built-in max()
as:
>>> max([1, 5, 2, 10, 4])
10