Implementing read and update in the model

Our entire design up to this point has been centered around a form that only appends data to a file; adding read and update capabilities is a fundamental change that will touch nearly every portion of the application. It may seem like a daunting task, but by taking it one component at a time, we'll see that the changes are not so overwhelming.

The first thing we should do is update our documentation, starting with the Requirements section:

The program must:

* Provide a UI for reading, updating, and appending data to the CSV file
* ...

And, of course, also update the part that is not required that follows:

The program does not need to:

* Allow deletion of data.

Now, it's a simple matter of making the code match with the documentation.

Adding read and update to our model

Open models.py and consider what's missing from the CSVModel class:

• We'll need a method that can retrieve all records in a file so we can display them. We'll call it get_all_records().
• We...