Understanding Python's “is” operator

Question

The is operator does not match the values of the variables, but the instances themselves.

What does it really mean?

Answer 1

A simple example with fruits

fruitlist = [" apple ", " banana ", " cherry ", " durian "]
newfruitlist = fruitlist
verynewfruitlist = fruitlist [:]
print ( fruitlist is newfruitlist )
print ( fruitlist is verynewfruitlist )
print ( newfruitlist is verynewfruitlist )

Output:

True
False
False

If you try

fruitlist = [" apple ", " banana ", " cherry ", " durian "]
newfruitlist = fruitlist
verynewfruitlist = fruitlist [:]
print ( fruitlist == newfruitlist )
print ( fruitlist == verynewfruitlist )
print ( newfruitlist == verynewfruitlist )

The output is different:

True
True
True

That's because the == operator compares just the content of the variable. To compare the identities of 2 variable use the is operator

To print the identification number:

print ( id( variable ) )