How can I check for NaN values?

Question

float('nan') represents NaN (not a number). But how do I check for it?

Answer 1

Use math.isnan:

>>> import math
>>> x = float('nan')
>>> math.isnan(x)
True

Answer 2

The usual way to test for a NaN is to see if it's equal to itself:

def isNaN(num):
    return num != num

Answer 3

numpy.isnan(number) tells you if it's NaN or not.

Answer 4

Here are three ways where you can test a variable is "NaN" or not.

import pandas as pd
import numpy as np
import math

# For single variable all three libraries return single boolean
x1 = float("nan")

print(f"It's pd.isna: {pd.isna(x1)}")
print(f"It's np.isnan: {np.isnan(x1)}}")
print(f"It's math.isnan: {math.isnan(x1)}}")

Output

It's pd.isna: True
It's np.isnan: True
It's math.isnan: True