Python complex four-function calculator

[lazyman353]

I am trying to make a four-function calculator as complex as possible and this is what I have so far what can I do to make it more complex

import sys
original_stdout = sys.stdout
def add(x, y):
    return x + y
def sub(x, y):
    return x - y
def mul(x, y):
    return x * y
def dev(x, y):
    return x / y
operations = ['+', "-", '*', '/']
while True:
    operation = input('pick an operation (+, -, *, /): ')
    while operation not in operations:
        operation = input('pick an operation (+, -, *, /): ')
    if operation == '+':
        print('you selected addition')
        x = int(input('please select first number: '))
        y = int(input('please select second number: '))
        call = add(x, y)
        with open('output.txt', 'a') as f:
            sys.stdout = f
            print('the anwser is:')
            print(call)
            sys.stdout = original_stdout
    elif operation == '-':
        print('you selected subtraction')
        x = int(input('please select first number: '))
        y = int(input('please select second number: '))
        call = sub(x, y)
        with open('output.txt', 'a') as f:
            sys.stdout = f
            print('the anwser is:')
            print(call)
            sys.stdout = original_stdout
    elif operation == '*':
        print('you selected multiplication')
        x = int(input('please select first number: '))
        y = int(input('please select second number: '))
        call = mul(x, y)
        with open('output.txt', 'a') as f:
            sys.stdout = f
            print('the anwser is:')
            print(call)
            sys.stdout = original_stdout
    elif operation == '/':
        print('you selected division')
        x = int(input('please select first number: '))
        y = int(input('please select second number: '))
        call = dev(x, y)
        with open('output.txt', 'a') as f:
            sys.stdout = f
            print('the anwser is:')
            print(call)
            sys.stdout = original_stdout