奇怪的行为：熊猫数据框中的一个numpy nan显示为dtype（'float64'）

Question

I am working on a dataframe that has many custom functions, libraries, and calculations. After doing some critical calcs, I noticed some errors in calculations that should have returned a float:

To inspect one of the calculations, I do the following.

dFA.loc['20101120']['variable x']

which returns ( in small caps )

nan

Then, to confirm that this thing is what looks like a weird (small caps) numpy.nan ( True or False ) I do:

dFA.loc['20101120']['variable x'] == np.nan

Which returns:

False

Then I do:

dFA.loc['20101120']['variable x'].dtype

Which returns:

dtype('float64')

Also:

dFA.loc['20101120']['variable x'] > 1000
False

Also:

dFA.loc['20101120']['variable x'] < 1000
False

Answer 1

 dFA.loc['20101120']['variable x'] == np.nan 

Oops. NaN is never equal to NaN.

np.isnan(dFA.loc['20101120']['variable x'])

Answer 2

All comparisons with np.nan evaluate to False by definition .

>>> np.nan == np.nan
False
>>> np.nan <= 1
False
>>> np.nan > 1
False

np.nan is a float:

>>> np.nan.__class__
<type 'float'>

... just a very special one.