Existence from the viewpoint of Python

What is identical to itself exists, otherwise not.

Pythonic Zen:

world = [0, 1, 2, 3, float("nan")]
[x for x in world if x == x]

Result:

[0, 1, 2, 3]

Explanation

According to IEEE754 (or PEP754),

$\forall$ X, NaN != X.

Thus Nan != Nan.

See also

• What is the rationale for all comparisons returning false for IEEE754 NaN values?
• PEP 754 -- IEEE 754 Floating Point Special Values