# import the pandas library
import pandas as pd
import numpy as np

df = pd.DataFrame(np.random.randn(2, 2),
                  index=['1', '3'],
                  columns=['key_1', 'val_1']
                  )

df = df.reindex(['1', '2', '3'])

print(df)
# todo how to handle NaN?

# import the pandas library
import pandas as pd
import numpy as np

df = pd.DataFrame(np.random.randn(2, 2),
                  index=['1', '3'],
                  columns=['key_1', 'val_1']
                  )

df = df.reindex(['1', '2', '3'])

print(df)
# todo how to handle NaN?

# import the pandas library # todo how to handle NaN?