Division by zero error, I reccomend putting a try function to prevent errors from appearing and messing up the script.

try:
    choice = input("Enter choice(1/2/3/4): ")
    num1 = float(input("Enter first number: "))
    num2 = float(input("Enter second number: "))
    if choice == '1':
       print(num1,"+",num2,"=", add(num1,num2))
    elif choice == '2':
       print(num1,"-",num2,"=", subtract(num1,num2))
    elif choice == '3':
       print(num1,"*",num2,"=", multiply(num1,num2))
    elif choice == '4':
       print(num1,"/",num2,"=", divide(num1,num2))
    else:
       print("Invalid input")
except:
    print("An error occured!")