CODEWITHSUNDEEP
pythonif-statementlogical-operators
Tom Kurushingal
Tom Kurushingal

Reputation: 6486

Why can't logical operators be used with relational operators in Python?

I am trying to compare if two different variables lie in two different ranges in Python using the logical operator '&' and the relational operator 'if'. The question might be a silly one and I am sure it will be down voted but even then why doesn't this code work?

Code

a = 2.0
b = 3.0

if 1 <= a <= 4 & 2 <= b <= 5:
    print 'Yes'

if 1 <= a <= 4:
    print 'Yes, a'

if 2 <= b <= 5:
    print 'Yes, b'

Output

Yes, a
Yes, b

And what is the best method to do such comparisons?

Upvotes: 0

Views: 768

Answers (4)

Shashank
Shashank

Reputation: 13869

and is boolean AND. & is bitwise AND.

Because bitwise AND has higher precedence (i.e. it is more binding) than the <= operator, it gets evaluated first when you don't wrap the left and right boolean comparison expressions in parentheses.

So the evaluation is like:

1 <= a <= 4 & 2 <= b <= 5

1 <= 2.0 <= (4 & 2) <= 3.0 <= 5

1 <= 2.0 <= 0 <= 3.0 <= 5

Which is obviously False. What you want is:

1 <= a <= 4 and 2 <= b <= 5

And you don't need parentheses here because theand operator has lower precedence than <= so the left and right expressions will get evaluated first by default.

It's worth taking a look at the operator precedence table. You don't need to memorize it, but it's good for understanding all the Python operators and their general relationship to one another.

Upvotes: 3

solinvictus
solinvictus

Reputation: 177

& is a bitwise operator.Use and instead of &.

if 1 <= a <= 4 and 2 <= b <= 5:
    print 'Yes'

Upvotes: 0

Dan D.
Dan D.

Reputation: 74645

Consider:

>>> a = 2.0
>>> b = 3.0
>>> 
>>> if 1 <= a <= 4 & 2 <= b <= 5:
...     print 'Yes'
... 
>>> if 1 <= a <= 4 and 2 <= b <= 5:
...     print 'Yes'
... 
Yes

Upvotes: 1

Wang HongQin
Wang HongQin

Reputation: 303

Note that & is a bitwise operator instead of a logical operator.

In python, logic operators consist of keyword and, or and not. In your case:

if 1 <= a <= 4 and 2 <= b <= 5:
    print 'Yes'

Upvotes: 0

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