Why does "np.NaN!=np.NaN" ?

Question

In the Data Science course under the missing numbers project, they use np.NaN. If they discuss that elsewhere in the course I missed it. My code didn't work and I ended up realizing that not matter how I wrote it, "print(np.NaN!=np.NaN)" always returned "True". Switching to None caused as error as the final array was of type Object rather than Float and I couldn't get astype() to work. Eventually, I just got fed up and defined a variable nan as a random float and my code worked as expected. While I now know there is a np.isnan exists, I would like to know what happened.

*Edit* I understand now that it is defined to not be equal. Any insight as to why it was defined that way?

Answer 1

Jon You cannot use equality test on NaN. Also nan, NaN and NAN are all aliases of the same thing.

See the following for more detail

https://numpy.org/doc/stable/user/misc.html?highlight=numpy%20nan

Answer 2

nan is defined to not equal itself, therefore isnan() to check if a valie is not a number.