Optional Choices

The optional choice field is desiged to offer a set of default choices or allow, optionally, to enter a custom value. The custom value has to conform to a specified field.

Here is an example of creating such a field:

>>> import zope.schema
>>> from z3c.schema.optchoice import OptionalChoice

>>> optchoice = OptionalChoice(
...     title=u'Occupation',
...     values=(u'Programmer', u'Designer', u'Project Manager'),
...     value_type=zope.schema.TextLine())

Note that the value type must be a field:

>>> OptionalChoice(
...     title=u'Occupation',
...     values=(u'Programmer', u'Designer', u'Project Manager'),
...     value_type=object())
Traceback (most recent call last):
ValueError: 'value_type' must be field instance.

Let’s now ensure that we can validate not only choices, but also custom values:

>>> optchoice.validate(u'Programmer')
>>> optchoice.validate(u'Project Manager')
>>> optchoice.validate(u'Scripter')

>>> optchoice.validate(u'Scripter\nHTML\n')
Traceback (most recent call last):
...
ConstraintNotSatisfied: Scripter
HTML

Let’s now ensure that we can convert values from unicode to a real value as well. To demonstrate this feature, we have to create a more restrictive optional choice field:

>>> optchoice = OptionalChoice(
...     title=u'Age',
...     values=(10, 20, 30, 40, 50),
...     value_type=zope.schema.Int(min=0))

>>> optchoice.fromUnicode(u'10')
10
>>> optchoice.fromUnicode(u'40')
40
>>> optchoice.fromUnicode(u'45')
45

>>> optchoice.fromUnicode(u'-10')
Traceback (most recent call last):
...
TooSmall: (-10, 0)

Reference