What are nested Dictionaries ?
                          A nested dictionary is a dictionary that contains one or more dictionaries as values.

Example :
Python 
students = { 1: {"name": "Rahul", "age": 22}, 2: {"name": "Anita", "age": 21} }

Creation :
Python 
student = { "name": "Rahul", "marks": { "python": 90, "math": 88 } }
Here, "marks" key holds another dictionary

Accessing :
Python 
student = { "name": "Rahul", "marks": { "python": 90, "math": 88 } } print(student["marks"]["python"]) #output 90

Updating :
Python 
student = { "name": "Rahul", "marks": { "python": 90, "math": 88 } } student["marks"]["math"] = 92 print(student) #output { "name": "Rahul", "marks": { "python": 90, "math": 92 } }

Deleting :
Python 
student = { "name": "Rahul", "marks": { "python": 90, "math": 88 } } del student["marks"]["python"]