Functions

Functions

The Python scripts that you tried in the previous chapter are executed
line by line. Each line of code performs one action and, after the action
is finished, execution moves to the next line. This is a simple and robust
way to perform tasks that straightforwardly proceed from the beginning
to the end.
However, if we want the user to decide what to do, instead of letting
the program always perform the same operations in the same order,
the code must be structured differently. Typically, this is the case when
an application has a graphical user interface that lets the user perform
different actions by interacting with user interface (UI) elements.
When using the S60’s framework for building user interfaces, the
execution does not progress deterministically line after line in the code.
Instead, the user may launch specific tasks by pressing, say, specific keys
on the mobile phone keyboard. In this case, your job as an application
developer is to bind specific tasks to specific key events. When the user
chooses a menu item or to quit, your application should execute a task
that corresponds to such an event. For this purpose, you need to make
functions of your own.
In Example 1 (shown here once more as Example 9), we had three
lines of code that were executed in sequence. The second line triggered
a text input field and the third line a popup note.