My Second Calculator

my_second_calculator.py

# My second calculator
print('Calculator loading... please wait')
add = {i:{j:i+j for j in range(1000)} for i in range(1000)}
sub = {i:{j:i-j for j in range(1000)} for i in range(1000)}
mult = {i:{j:i*j for j in range(1000)} for i in range(1000)}
div = {i:{j:i/j for j in range(1,1000)} for i in range(1000)}

print('''
Welcome to my calculator!
Please make a selection
a: Addition
s: Subtraction
m: Multiplication
d: Division''')

selection = input('a,s,m,d: ')
if selection == 'a':
    operation = add
if selection == 's':
    operation = sub
if selection == 'm':
    operation = mult
if selection == 'd':
    operation = div

first_number = input('please enter the first number')
second_number = input('please enter the second number')

print('Your result is:')
print(operation[int(first_number)][int(second_number)])