Why is float('nan') not equal to itself in python

Question

This question already has answers here: question from:https://stackoverflow.com/questions/65895670/different-kinds-of-nan-in-python

Answer 1

There are two reasons, one practical and one historical. The historical reason is that this makes it trivial to test for a NaN. If the value isn't equal to itself, it's a NaN.

The practical reason is that NaN is used to indicate various different cases where the value is not defined, and not all undefined values are equal.

Should NaN/NaN equal 1? Think about how crazy that would be. Arguing that NaN should equal itself is only a bit less crazy.