Implementing XOR in Python

Question

So I'm trying to implement the logical operator XOR in Python. I first ask the user for how many inputs they want to test (4 - TT, TF, FT, FF). I know that XOR evaluates T&T->F, T&F->T, F&T->T, F&F->F.

I store the first boolean that I get as input from the user in a variable P as a string. I then convert to boolean. As so...

    P = input("Enter boolean number 1: ")
    P = bool(P)

I don't cast the input as bool right away since any non-empty string will result in True regardless of the string being "False."

I have the XOR truth table established for the four possible conditions mentioned above as four separate if statements and then just print("P xor Q is False" or "P xor Q is True") all depending on the truth table for XOR.

All this logic is inside a for loop that counts down by 1 until 0 from the user's input of how many inputs they wanted to make.

When I run this program, regardless of what the user enters, the print statement is "P xor Q is False."

I just can't figure out why! I feel the solution is pretty simple which is what is bothering me, so any help in the right direction would be appreciated, thank you!

Here's my code:

numOfInputs = int(input("Enter the number of inputs: "))

for num in range(numOfInputs, 0, -1):
    print()

    P = input("Enter the first boolean: ")
    P = bool(P)
    Q = input("Enter the second boolean: ")
    Q = bool(Q)

    print()

    if(P == True and Q == True):
        print("P xor Q is False")
    if(P == True and Q == False):
        print("P xor Q is True")
    if(P == False and Q == True):
        print("P xor Q is True")
    if(P == False and Q == False):
        print("P xor Q is False")

Answer 1

Both T and F are "true" as any non-empty string is "true" in Python. This might explain why your loop isn't working as expected.

The first step is to fix your casting:

p = input('Enter a boolean value, True or False: ')
if p.lower() == 'false':
   p = False
q = input('Enter the second boolean, True or False: ')
if q.lower() == 'false':
   q = False

Now, a XOR is simply when two values do not equal each other:

if p != q:
   print('p xor q is true')
else:
   print('p xor q is false')

Answer 2

Your code works fine if you use an empty string for False, i.e. just press return.

An empty string is the only string value which bool converts to False:

>>> bool('False')
True

>>> bool('0')
True

>>> bool('')
False

See the documentation.

If you're not using strings Python considers 0, {}, [], to all be equivalent to False, i.e. zero or empty containers. Most other things are True.

If you want to use any of those as input you can convert the string value to the actual type using ast.literal_eval, then convert to a bool to get True or False.

>>> import ast.literal_eval
>>> value = literal_eval('False')
>>> type(value)
bool
>>> value
False

>>> value = literal_eval('0')
>>> type(value)
int
>>> bool(value)
False

Your boolean comparisons can be simplified, e.g.:

if(P == True and Q == False):
    print("P xor Q is True")

could be:

if P and not Q:
    print("P xor Q is True")