Please explain this code:

Question

https://code.sololearn.com/cz6jP4XEwnKI/?ref=app

According to what i understand, pi will first evaluate _s3 == s2_, which clearly is _True_, but then it evaluates _s1 is True_ and gives result as _True_ when it should be _False_!?

Answer 1

s1 = 'abc'
s2 = input() # enter abc
s3 = 'abc'

print(s1 is s3 == s2)
# This reads as <s1> is <s3> AND <s3> == <s2>
# <s1> is <s3> checks for reference equality -> True
# <s3> == <s2> checks for content equality -> True

print(s3 == s2)
# <s3> == <s2> checks for content equality -> True

print(s1 is True)
# checks for reference equality -> False

# To verify <s1> and <s3> refers to
# same object you can check their ID
#print(id(s1), id(s2), id(s3))

Hth, cmiiw

Answer 2

Thanks a lot for explaining Ipang. If there is an _AND_ in between this makes it a lot simpler.

But why is there an _AND_ there? Why wouldn't python just evaluate the equality and then the identity?

And what is Hth, cmiiw?

Answer 3

Anirudh Sharma
Actually I didn't understand either, in the first place. Then I remember Python allows compound comparison like `a < b < c` which is evaluated (as you probably know already) as `a < b AND b < c`.

Then It came to me the evaluation of `s1 is s3 == s2` looks pretty much the same. And turned out it makes just the sense : )

"Why wouldn't Python just evaluate the equality and then identity?"

I don't have the answer to that question apparently.

Hope That Helps, Correct Me If I'm Wrong => Hth, cmiiw

Answer 4

Ipang, you are awesome, your explanation is perfect. This issue was troubling me for days, i thought py was useless as it would develop similar issues in bigger formulae; instead it turn out to be better in terms of compound comparison!!

Tal,thal

Answer 5

You're welcome, I'm glad if it helps : )