CODEWITHSUNDEEP
python
Harvey
Harvey

Reputation: 1418

What is the correct method of performing an 'Or' operation in an 'If' Statement? - Python

I have an If staement that is not behaving as I would have intended.

Here is my example:

if not userTime[-2].upper() == "X" or not userTime[-2].upper() == "Z":
        raise ValueError("not entered an X or a Z")
else:
        notValid = False

My input would always result in userTime[-2] always being a capital 'Z'

Printing out the userTime[-2].upper() to the screen appears as a 'Z' Yet it still raises the exception.

I cannot get it to hit the else part of this 'if' statement and am now wondering if there is something I have missed out

Upvotes: 1

Views: 71

Answers (1)

Kevin
Kevin

Reputation: 76254

The opposite of a or b isn't not a or not b, it's not a and not b. Try:

if not userTime[-2].upper() == "X" and not userTime[-2].upper() == "Z":

Or, equivalently,

if userTime[-2].upper() != "X" and userTime[-2].upper() != "Z":

Or, avoiding the issue of complex boolean expressions entirely,

if userTime[-2].upper() not in ("X", "Z"):

Negating boolean expressions is a bit counterintuitive. Consult De Morgan's laws for more information.

Upvotes: 6

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