in most applicationsyou can further break down the second step of modifying the in-memory presentation of the data an application can provide some or all of these features as part of the modification processprovide an onscreen presentation of the data allow additions to the data list allow deletions from the data list make changes to existing datawhich can actually be implemented by adding new record with the changed data and deleting the old record so far in this you have performed all but one of the activities in these two lists you've already read file content and written file content in the modification listyou've added data to list and presented the data onscreen the only interesting activity that you haven' performed is deleting data from list the modification of data is often performed as two-part process of creating new record that starts with the data from the old record and then deleting the old record after the new record is in place in the list don' get into rut by thinking that you must perform every activity mentioned in this section for every application monitoring program wouldn' need to display the data onscreen in factdoing so might be harmful (or at least inconvenienta data logger only creates new entries -it never deletes or modifies them an -mail application usually allows the addition of new records and deletion of old recordsbut not modification of existing records on the other handa word processor implements all the features mentioned what you implement and how you implement it depends solely on the kind of application you create separating the user interface from the activities that go on behind the user interface is important to keep things simplethis example focuses on what needs to go on behind the user interface to make updates to the file you created in the "creating filesectionearlier in this the following steps demonstrate how to readmodifyand write file in order to update it the updates consist of an additiona deletionand change to allow you to run the application more than oncethe updates are actually sent to another file this example also appears with the downloadable source code as formatteddata py and updatecsv py open python file window you see an editor in which you can type the example code type the following code into the window -pressing enter after each linefrom formatteddata import formatdata import os path