I create menu in Python but get eror

Question

I get error after debugging. The error is ("NameError: name 'raw_input' is not defined). Can help me with this error?

ans=True
while ans:
    print("""
    1.Add a Student
    2.Delete a Student
    3.Look Up Student Record
    4.Exit/Quit
    """)
    ans=raw_input("What would you like to do? ")
    if ans=="1":
      print("\nStudent Added")
    elif ans=="2":
      print("\n Student Deleted")
    elif ans=="3":
      print("\n Student Record Found")
    elif ans=="4":
      print("\n Goodbye") 
      ans = None
    else:
       print("\n Not Valid Choice Try again")