Tryton allows developers to define methods that can be called once a field’s value has changed by the user this is the on_change method. The method has the following name:
Model.on_change_<field name>
This is an instance method, an instance of Model will be created by using
the values from the form’s fields specified by the on_change list defined
on the field. Any change made on the instance will be pushed back to the
client-side record.
There is also a way to define a method that must update a field whenever any field from a predefined list is modified. This list is defined by the on_change_with attribute of the field. The method that will be called has the following name:
Model.on_change_with_<field_name>
Just like for the classic on_change, an instance of Model will be
created by using the values entered in the form’s fields specified by the
on_change_with attribute. The method must return the new value of the field
to push back to the client-side record.