Develop a Python code to compute the maximum of 3 numbers
number1 = 33
number2 = 12
number3 = 19
def maximum_of_three(number1,number2,number3):
max_value = number1
if number2 > max_value:
    max_value = number2
if number3 > max_value:
    max_value = number3
return max_value