Python – How to Check List Containing NaN

python

In my for loop, my code generates a list like this one:

list([0.0,0.0]/sum([0.0,0.0]))

The loop generates all sort of other number vectors but it also generates [nan,nan], and to avoid it I tried to put in a conditional to prevent it like the one below, but it doesn't return true. 

nan in list([0.0,0.0]/sum([0.0,0.0]))
>>> False

Shouldn't it return true?

enter image description here

Libraries I've loaded:

import PerformanceAnalytics as perf
import DataAnalyticsHelpers
import DataHelpers as data
import OptimizationHelpers as optim
from matplotlib.pylab import *
from pandas.io.data import DataReader
from datetime import datetime,date,time
import tradingWithPython as twp
import tradingWithPython.lib.yahooFinance as data_downloader # used to get data from yahoo finance
import pandas as pd # as always.
import numpy as np
import zipline as zp
from scipy.optimize import minimize
from itertools import product, combinations
import time
from math import isnan

Best Answer

I think this makes sense because of your pulling numpy into scope indirectly via the star import.

>>> import numpy as np
>>> [0.0,0.0]/0
Traceback (most recent call last):
  File "<ipython-input-3-aae9e30b3430>", line 1, in <module>
    [0.0,0.0]/0
TypeError: unsupported operand type(s) for /: 'list' and 'int'

>>> [0.0,0.0]/np.float64(0)
array([ nan,  nan])

When you did

from matplotlib.pylab import *

it pulled in numpy.sum:

>>> from matplotlib.pylab import *
>>> sum is np.sum
True
>>> [0.0,0.0]/sum([0.0, 0.0])
array([ nan,  nan])

You can test that this nan object (nan isn't unique in general) is in a list via identity, but if you try it in an array it seems to test via equality, and nan != nan:

>>> nan == nan
False
>>> nan == nan, nan is nan
(False, True)
>>> nan in [nan]
True
>>> nan in np.array([nan])
False

You could use np.isnan:

>>> np.isnan([nan, nan])
array([ True,  True], dtype=bool)
>>> np.isnan([nan, nan]).any()
True
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