Dictionaries are equivalent to Hash Data Structure in some languages
Contact list
* Can directly get a person’s number from his name, without searching
* Contact records can have lot of fields, many of which might be empty. If we represent contact record as a list/tuple, will be difficult to keep track of the fields. Better to represent the information a dictionary of dictionaries or as list of dictionaries
Since mydict has a List as its element , it is not allowed as dictionary key.
The list may change in future hence inappropriate for a dict key
Use del operator to delete an element in dictionary