What's the difference between nan, NaN and NAN

问题

In numpy there are nan, NaN and NAN. What's the sense of having all three, do they differ or any of these can be used interchangeably?

回答1:

>>> numpy.nan is numpy.NaN is numpy.NAN
True

It's just convenient. They're exactly the same.

回答2:

Different operating systems and programming languages may have different string representations of NaN:

 nan  
 NaN  
 NaN%  
 NAN  
 NaNQ  
 NaNS  
 qNaN  
 sNaN
 1.#SNAN
 1.#QNAN  
 -1.#IND

I think having all three is just a convenience. They are the same.

>>> np.nan
nan
>>> np.NaN
nan
>>> np.NAN
nan
>>> 

来源：https://stackoverflow.com/questions/17825707/whats-the-difference-between-nan-nan-and-nan