The is Operator

About the interned numbers (am I spelling that right?) I noticed that the id’s for ‘x = 20’ was the same, even after I exited Python and started a new REPL. I was expecting the assignments to occur when the REPL started, but I suppose not. So what’s determining the id’s for -5 to 256? My OS?

@jamesbrown68 hmm, that’s really interesting! I don’t get that behavior with my REPL, and interning is generally only preserved over each invocation of Python, so I’m not sure what’s causing that to happen. Out of curiosity, what OS and REPL are you running?

I’m on Windows 10, Python 3.8.1.

python
>>> x = 20
>>> id(x)
1617684704
exit()
python
>>> x = 20
>>> id(x)
1617684704

Wow @jamesbrown68, I have to admit this one stumps me. I wonder if there’s some system setting in your OS that’s causing Python to run in exactly the same way every time?

Wondering why I’m getting this output?

[root@vedang]# python
Python 2.7.5 (default, Aug  7 2019, 00:51:29)
[GCC 4.8.5 20150623 (Red Hat 4.8.5-39)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> a = "hello"
>>> b = "hello"
>>> a is b
True
>>> a == b
True
>>> id(a)
140575040349312
>>> id(b)
140575040349312
>>>

the interning feature seems random?

“Interning is an implementation-dependent optimization that depends on many factors. It can be interesting to understand how it works, but never depend on it working any particular way.” (Source)

i have not been able to recreate the above example.

a='bro!'
b='bro!'
print(a is b)

a='bro '
b='bro '

print(a is b)

True
True

[Program finshed]

nevermind

a='bro'
b='bro'
print(a is b)

a=a+'!'
b=b+'!'

print(a is b)

True
False

[Program finished]

nevermind

a='bro'
b='bro'
print(a is b)

a=a+'!'
b=b+'!'

print(a is b)

True
False

[Program finished]

is this use case safe?

if a is True:

Hi @lordcommandermay,

Whether it’s safe, depends on what you’re doing within in if statement. But checking if an object is True is common in Python. However, if you are checking to see if the presence of the object a, then you can shorten it to just: if a:. If a is a boolean, and you want to check it’s truthiness, then you should use == instead of is. Hope that helps.