SW is a pin component (just look at the schematics). So you need to look into the pin component data sheet. There you will find the _read() method.
Thank you very much hli, I got lost with "SW" name on the pin name, it si very trival !!!!
Naming the pin components for their purpose is good practice, though it can be confusing sometimes...
You can always use a functional name combined with physical name
and get an easily understood pin name.