Magic Number in Python

Question

In the following code :

magicnumber = 256
for n in range (500):
    if n is magicnumber:
        print ("the magic number is " , n)
        break
    else:
        print(n)

The loop breaks at 256, but if you set magicnumber to 257, it doesn't. Why ?

OK run the code below and the return value will be zero magicnumber = 257 for n in range (500): if n is magicnumber: print ("the magic number is " , n) — TheOraclePhD, Oct 13 '18 at 15:22
`n is magicnumber` -> `n == magicnumber` ([see here](https://stackoverflow.com/questions/306313/is-operator-behaves-unexpectedly-with-integers)) — Yaroslav Admin, Oct 13 '18 at 15:23
Your answer is correct but can you explain it to me what is the difference between is and equal? — TheOraclePhD, Oct 13 '18 at 15:28

score 6 · Accepted Answer · answered Oct 13 '18 at 15:22

Because you are checking for identity with is (instead of checking for equality with ==).

As an implementation detail, Python keeps an array of integer objects for all integers between -5 and 256, when you create an int in that range you actually just get back a reference to the existing object.

So integers above 256 will still be equal, but not identical (unless they refer to the same object, you can compare that with id()).

Source: https://docs.python.org/3/c-api/long.html#c.PyLong_FromLong

Magic Number in Python

1 Answers1