Python - else statement is never triggered

I would expect this to be a duplicate question, yet I couldn't find an answer. I'm sorry.

I have written a simple function that's supposed to return either an empty string or a string of one character. Sometimes, however, it returns None. Even though it should match one of the operands and, in case it doesn't, still output a string.

baseconvert = digits+ascii_lowercase+"0"
def checker(operand, factorlist): # hardcoded interpreter of the calculus converted in base 10. i is equal to the base.
    if (operand == '+'):
        if (factorlist[0] + factorlist[1] == factorlist[2]):
            return baseconvert[i]
    elif (operand == '-'):
        if (factorlist[0] - factorlist[1] == factorlist[2]):
            return baseconvert[i]
    elif (operand == '*'):
        if (factorlist[0] * factorlist[1] == factorlist[2]):
            return baseconvert[i]
    elif (operand == '/'):
        if (factorlist[0] / factorlist[1] == factorlist[2]):
            return baseconvert[i]
    else:
        return ""

So while typing this post I figured out I could just remove the else statement:

    # else: is not necessary
    return ""

works fine. I still wonder, however, why this else statement is never triggered.

P.S.: Is there a cleaner way to just interpret the string, for example "10 - 7 = 3" to get a boolean result? I'm relatively new to python and couldn't come up with anything.