import pandas as pd
import numpy as np

users = [('Ali', 'M', 'Lahore', 20000),
            ('Jhon', 'M', 'Dubai', 25000),
            ('Wick', 'M', np.nan, 40000),
            ('Harry', 'M', 'Manchester', 35000),
            ('Snape', 'M', 'Hogwards', 30000),
            ('Hermoine', 'F', np.nan, 20000),
            ('Ayesha', 'F', 'Karachi', 24000),
            ('Julie', 'F', np.nan, 70000)
            ]

# Create a sample dataframe and setting name as index column
df = pd.DataFrame(users, columns =['Name', 'Sex','City', 'Income'])
df.set_index("Name", inplace = True)

df["City"].fillna("No Data Available", inplace = True)
print(df)