Type MessageID

object --+                
         |                
   Element --+            
             |            
     Attribute --+        
                 |        
             Field --+    
                     |    
        object --+   |    
                 |   |    
         MinMaxLen --+    
                     |    
                  Text --+
                         |
                        MessageID

Text string that should be translated.

When a string is converted to a message ID, it is also recorded in the context.

>>> class Info(object):
...     file = 'file location'
...     line = 8

>>> class FauxContext(object):
...     i18n_strings = {}
...     info = Info()

>>> context = FauxContext()
>>> field = MessageID().bind(context)

There is a fallback domain when no domain has been specified.

Exchange the warn function so we can make test whether the warning has been issued

>>> warned = None
>>> def fakewarn(*args, **kw):
...     global warned
...     warned = args

>>> import warnings
>>> realwarn = warnings.warn
>>> warnings.warn = fakewarn

>>> i = field.fromUnicode(u"Hello world!")
>>> i
u'Hello world!'
>>> i.domain
'untranslated'
>>> warned
("You did not specify an i18n translation domain for the '' field in file location",)

>>> warnings.warn = realwarn

With the domain specified:

>>> context.i18n_strings = {}
>>> context.i18n_domain = 'testing'

We can get a message id:

>>> i = field.fromUnicode(u"Hello world!")
>>> i
u'Hello world!'
>>> i.domain
'testing'

In addition, the string has been registered with the context:

>>> context.i18n_strings
{'testing': {u'Hello world!': [('file location', 8)]}}

>>> i = field.fromUnicode(u"Foo Bar")
>>> i = field.fromUnicode(u"Hello world!")
>>> from pprint import PrettyPrinter
>>> pprint=PrettyPrinter(width=70).pprint
>>> pprint(context.i18n_strings)
{'testing': {u'Foo Bar': [('file location', 8)],
             u'Hello world!': [('file location', 8),
                               ('file location', 8)]}}

>>> from zope.i18n.messageid import MessageID
>>> isinstance(context.i18n_strings['testing'].keys()[0], MessageID)
1

Explicit Message IDs

>>> i = field.fromUnicode(u'[View-Permission] View')
>>> i
u'View-Permission'
>>> i.default
u'View'

>>> i = field.fromUnicode(u'[] [Some] text')
>>> i
u'[Some] text'
>>> i.default
u'[Some] text'