pandas.isnull(obj) Method
The isnull() method returns a True or False value. Where, True means that there is some missing data and False means that the data is not null. True and False are treated as 1 and 0 respectively.
pandas.isnull().sum().sum() Method
The sum() method returns the count of True values generated from the isnull() method.
Here, you have to use the sum() method twice to count the NaN values in the entire dataset. First, it will count the NaN values in each column and the second time it will add all the NaN values from all the columns.
To work with MultiIndex in Python Pandas, we need to import the pandas library. Below is the syntax,
import pandas as pd
Let us understand with the help of an example.
Output:

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