django-like-contactform.py

# Django-like implementation

class BoundField(object):
    def __init__(self, form, field, name):
        self.form = form
        self.field = field
        self.name = name
    def _data(self):
        return self.field.value_from_datadict(self.form.data, self.name)
    data = property(_data)

class CharField(object):
    def value_from_datadict(self, data, text):
        return data.get(text, None)
    
class DeclaredMetaFields(type):
    def __new__(cls, name, bases, attrs):
        fields = [(field_name, attrs.pop(field_name)) for field_name, obj in attrs.items() if isinstance(obj, CharField)]
        attrs['fields'] = dict(fields)
        return type.__new__(cls, name, bases, attrs)

class Form(object):
    __metaclass__ = DeclaredMetaFields
    
    def __init__(self, data=None):
        self.data = data or {}
    
    def __getitem__(self, name):
        try:
            field = self.fields[name]
        except KeyError:
            raise KeyError('Key %r not found in Form' % name)
        return BoundField(self, field, name)

class ContactForm(Form):
    first_name = CharField()
    last_name = CharField() 
    email = CharField()

c = ContactForm({'first_name':'James', 'last_name':'Bond'})
# The following line prints 
# James Bond
print c['first_name'].data, c['last_name'].data