逻辑门：x！= Python中的'减号'或'加号'

Question

I've got a strange syntactical situation going on in an if...then statement. Not really sure what the fix is...

x1 = 'minus'
if x1 == 'minus':
    print('OK')
if x1 != 'minus':
    print('this should not print')

y = {'direction':'minus'}
x2 = y['direction']
if x2 != 'plus' or x2 != 'minus':
    print("huh...")
if x1 != 'plus' or x1 != 'minus':
    print("??")
if x1 == 'plus' or x1 == 'minus':
    print("wait...")
print(x2)
if (x2 != 'plus') or (x2 != 'minus'):
    print("it wasn't the parenthesis...")

print(x2 != 'plus')
print(x2 != 'minus')

print(x2)

Output is:

>OK
>huh...
>??
>wait...
>it wasn't the parethesis...
>True
>False
>minus

How do I create a logic gate in python that will only trigger if x != 'minus' or 'plus' in python?

Answer 1

How do I create a logic gate in python that will only trigger if x != 'minus' or 'plus' in python?

x is always not equal to one of those (think about it: if it's plus , that test isn't true—but plus is not minus , so the other test is true), so using or as you have will always be true!

What you probably want is something like this:

if not (x == 'minus' or x == 'plus')

Applying De Morgan's Law, you could also use:

if x != 'minus' and x != 'plus'

You can also use the more Pythonic:

if x not in ('minus', 'plus')