Welcome to our exploration of Compound Data Structures in Python. Having navigated through Dictionaries, Sets, and Tuples, we'll delve into nested dictionaries and lists. These structures enable us to handle complex and hierarchical data, which is typical in real-world scenarios. This lesson will guide you through a recap of the basics, the creation and modification of nested dictionaries and lists, as well as common error handling.

As a quick recap, Lists are mutable, ordered collections, while Dictionaries are collections of key-value pairs. These structures can be nested. Here's a simple example of a school directory:

Just like their non-nested versions, creating nested structures is straightforward.

Nested Dictionary:

Nested List:

Nested Dictionary and Lists:

The retrieval of values from nested dictionaries or lists follows rules similar to those for their non-nested counterparts.

From Nested Dictionary:

From Nested List:

From Both:

The modification of nested lists and dictionaries is similar to that of non-nested versions.

Python executes exceptions effortlessly by providing the try/except blocks. The try block lets you test a block of code for errors, and the except block lets you handle the error. In the following example, we attempt to print a non-existent key in nested_dict. If the key is not found, a KeyError is raised, and the except block catches this error and executes its code.

In this code:

• The try block attempts to execute print(nested_dict['fruit']['mango']).
• If mango does not exist in nested_dict['fruit'], a KeyError is raised.
• The except KeyError block catches this error and prints "Key not found!" instead of stopping the program execution.

Bravo! You've made a journey through nested lists and dictionaries, terms that are becoming increasingly common in the data-intensive programming world. We've learned how to create, access, and modify values in these complex structures and how to handle errors.

Up next, we have hands-on practice sessions to solidify your understanding of these concepts. Hold on to your hats!