df = pd.DataFrame(randn(5, 3), index=['a', 'c', 'e', 'f', 'h'], columns=[
    'one', 'two', 'three'])
df = df.reindex(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'])
Best way to count the number of rows with missing values in a pandas DataFrame