Note: the Override tab is being phased out in favor of the TALES tab.
Sometimes you'd like a field property to be dynamic instead of
just a value filled in in the Edit tab of the field. If you fill
in the name of an override method for a property in the Override
tab, that method will be called whenever you (or the code) asks
for the value of that property using get_value(). Properties which
are overridden are shown between square brackets ([ and ]) in the
main Edit tab, and the value of the property in the edit tab will
be ignored. To stop using an override for a particular property,
remove the method name in the override tab.
An override method should return an object of the same type as the property field would return after validation. For instance, an override method for a StringField would return a simple string, for an IntegerField it would return an integer, and for a CheckBoxField it would return true or false (or something that can be interpreted that way).
A good example of the use of the override tab is the items
property of a ListField; frequently you may want to get these
items from elsewhere, for instance from a database. In this case
you would fill in the name of the override method for items that
retrieves the right data.
The right data in this case is that which validation of the
builtin field ListTextArea would return. This is a list of tuples,
one tuple for each element. Each tuple consists of two strings;
the name that should be displayed to the user for that item, and
the actual value that will be submitted.
This for instance is a Python script random_numbers that will return
ten random numbers as the elements:
# random_numbers
import random
result = []
for i in range(10):
number = random.randint(0, 100)
tuple = str(number), str(number)
result.append(tuple)
return result