Plone 4: Adding vocabulary to a Content Type field (Archetype)

A while back, I needed to use vocabularies with Archetypes. Being still new in Plone, I rummaged the internet for a while. This is the way I did it on Plone 4.

1. First, I create a vocab.py in the package's root, alongside configure.zcml, then put my vocabularies there:
   

   from zope.schema.vocabulary import SimpleVocabulary, SimpleTerm 
   
   def MyVocabulary(context): 
   
      items = [ 
        ("value1", u"This is label for item"), 
        ("value2", u"This is   label for value 2")] 
   
      terms = [ SimpleTerm(value=pair[0], token=pair[0], 
                        title=pair[1]) for pair in items ] 
   
      return SimpleVocabulary(terms) 

   
   A 'titled' vocabulary like this one will, for example, allow you to use a UID as a form's returned value but display a human-readable title by a checkbox.
   I've generally found it easiest to use the SimpleVocab classes.
2. This needs registering as a named IVocabularyFactory utility in configure.zcml:
   

    <utility 
            provides="zope.schema.interfaces.IVocabularyFactory" 
            component=".vocab.MyVocabulary" 
            name="MyVocabularyName" 
            /> 
   

3. Then you can use this in a schema:
   

   class MyWidgetSchema(interface.Interface): 
   
        categories = schema.Set( 
            value_type = schema.Choice(
                          vocabulary = u"MyVocabularyName", 
                          title = u"Favourite Things"), 
            default = set(), 
            title = u"Favourite Things" 
        ) 
   

   or

   atapi.StringField('item_favourite',
           required = 1,
           vocabulary_factory = u"MyVocabularyName",
           widget = atapi.SelectionWidget(
               label = _('Favourite Things'),
               description = _('Favourite Things'),
           ),
       ),
    

I hope this might help some poor soul out there.