Counting NaN values in a Pandas series with isna and sum

How many NaNs in a Python Pandas series? Use isna (returns True/False) then sum/value_counts:

s = pd.Series([10, 20, np.nan, 40, 50, np.nan, 70, 80])
s.isna().sum()          # returns 2
s.isna().value_counts() # count True/False

Hint: Pass normalize=True for the percentage