Example of where():

import pandas as pd
import numpy as np

df = pd.DataFrame({
    'EmpCode': ['Emp001', 'Emp002', 'Emp003', 'Emp004', 'Emp005'],
    'Name': ['John', 'Doe', 'William', 'Spark', 'Mark'],
    'Occupation': ['Chemist', 'Accountant', 'Statistician',
                   'Statistician', 'Programmer'],
    'Date Of Join': ['2018-01-25', '2018-01-26', '2018-01-26', '2018-02-26',
                     '2018-03-16'],
    'Age': [23, 24, 34, 29, 40]})

df['Department'] = pd.np.where(df.Occupation.str.contains("Chemist"), "Science",
                               pd.np.where(df.Occupation.str.contains("Statistician"), "Economics",
                               pd.np.where(df.Occupation.str.contains("Programmer"), "Computer", "General")))

print(df)

C:\pandas>python example48.py
   Age Date Of Join EmpCode     Name    Occupation Department
0   23   2018-01-25  Emp001     John       Chemist    Science
1   24   2018-01-26  Emp002      Doe    Accountant    General
2   34   2018-01-26  Emp003  William  Statistician  Economics
3   29   2018-02-26  Emp004    Spark  Statistician  Economics
4   40   2018-03-16  Emp005     Mark    Programmer   Computer
 
C:\pandas>