CODEWITHSUNDEEP
python
vorpal
vorpal

Reputation: 330

why doesn't 0 == (0 or 1) return True

My original bit of python was:

if i.count('<') and i.count('>') == (0 or 1):
    pass
else:
    print('error')

This passes with i = '<>' and fails with i = '<>>' which is what I want. However it also fails with i = '' which I don't want and can't understand.

In ipython3 i've fiddled with this long enough to come down to the abstracted

0 == (0 or 1)

which strangely returns False. I'm guessing it has something to do with 0=False 1=True, but even after quite a bit of googleing it still doesn't quite make sense to me.

Do I really have to rewrite my original code to the much longer and to my mind uglier:

(i.count('<') and i.count('>') == 0) or (i.count('<') and i.count('>') == 1)

Upvotes: 1

Views: 109

Answers (2)

falsetru
falsetru

Reputation: 369334

0 or 1 is always evaluated to 1 (The expression x or y first evaluates x; if x is true, its value is returned; otherwise, y is evaluated and the resulting value is returned. -- from Boolean operations)

>>> 0 or 1
1

0 == (0 or 1) is equivalent to 0 == 1 -> False.

To check whether x is 0 or 1, do the following:

x == 0 or x == 1

or

x in (0, 1)

Upvotes: 9

Jan Vorcak
Jan Vorcak

Reputation: 20019

(0 or 1) is evaluated to 1, 0 == 1 is evaluated to False

Upvotes: 2

Related Questions