Python if does not behave as expected

Question

I was trying to make a python calculator. But for some reason it will only output the square-root option.
I am currently using python3.4 and 3.3 emulator on my iPhone, but it has the same problem on both devices.

print("This program is a calculator app \n Creator: AtPython")
print("...")
Print("please choose a       mathematical operation")
Opt = input("square-root. \n addition, \n subtraction, \n multiplication, \n division: ")

if opt == "square-root" or "squareroot":
    num = float(input('Enter a number: '))
    num_sqrt = num ** 0.5
    print('The square root of %0.3f is %0.3f'%(num ,num_sqrt))
    input("Press 'Enter' to exit")

If opt == "addition":
    add_1 = float(input("Please enter a number"))
    add_2 = float(input("Please enter another number")) 
    add_ans = add_1 + add_2
    print(add_ans)
    qus = input("Would you like to add   another number? [y/n]")
    
elif qus == "y":
    add_3 = float(input("Enter a third number"))
    input("Press 'Enter' to exit")
    
else:
    input("Press 'Enter' to exit")