Added a `TypedChoiceField` which acts just like `ChoiceField`, except that it

returns a value coerced by some provided function. Refs #6967.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@8771 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/forms/fields.py

@@ -23,6 +23,7 @@ try:
 except NameError:
     from sets import Set as set
 
+import django.core.exceptions
 from django.utils.translation import ugettext_lazy as _
 from django.utils.encoding import smart_unicode, smart_str
 
@@ -39,6 +40,7 @@ __all__ = (
     'BooleanField', 'NullBooleanField', 'ChoiceField', 'MultipleChoiceField',
     'ComboField', 'MultiValueField', 'FloatField', 'DecimalField',
     'SplitDateTimeField', 'IPAddressField', 'FilePathField', 'SlugField',
+    'TypedChoiceField'
 )
 
 # These values, if given to to_python(), will trigger the self.required check.
@@ -657,6 +659,33 @@ class ChoiceField(Field):
                     return True
         return False
 
+class TypedChoiceField(ChoiceField):
+    def __init__(self, *args, **kwargs):
+        self.coerce = kwargs.pop('coerce', lambda val: val)
+        self.empty_value = kwargs.pop('empty_value', '')
+        super(TypedChoiceField, self).__init__(*args, **kwargs)
+        
+    def clean(self, value):
+        """
+        Validate that the value is in self.choices and can be coerced to the
+        right type.
+        """
+        value = super(TypedChoiceField, self).clean(value)
+        if value == self.empty_value or value in EMPTY_VALUES:
+            return self.empty_value
+        
+        # Hack alert: This field is purpose-made to use with Field.to_python as
+        # a coercion function so that ModelForms with choices work. However,
+        # Django's Field.to_python raises django.core.exceptions.ValidationError,
+        # which is a *different* exception than
+        # django.forms.utils.ValidationError. So unfortunatly we need to catch
+        # both.
+        try:
+            value = self.coerce(value)
+        except (ValueError, TypeError, django.core.exceptions.ValidationError):
+            raise ValidationError(self.error_messages['invalid_choice'] % {'value': value})
+        return value
+
 class MultipleChoiceField(ChoiceField):
     hidden_widget = MultipleHiddenInput
     widget = SelectMultiple

docs/ref/forms/fields.txt

@@ -362,6 +362,33 @@ Takes one extra required argument:
 
     An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this
     field.
+    
+``TypedChoiceField``
+~~~~~~~~~~~~~~~~~~~~
+
+.. class:: TypedChoiceField(**kwargs)
+
+Just like a :class:`ChoiceField`, except :class:`TypedChoiceField` takes an
+extra ``coerce`` argument.
+
+    * Default widget: ``Select``
+    * Empty value: Whatever you've given as ``empty_value``
+    * Normalizes to: the value returned by the ``coerce`` argument.
+    * Validates that the given value exists in the list of choices.
+    * Error message keys: ``required``, ``invalid_choice``
+
+Takes extra arguments:
+
+.. attribute:: TypedChoiceField.coerce
+
+    A function that takes one argument and returns a coerced value. Examples
+    include the built-in ``int``, ``float``, ``bool`` and other types. Defaults
+    to an identity function.
+
+.. attribute:: TypedChoiceField.empty_value
+
+    The value to use to represent "empty." Defaults to the empty string;
+    ``None`` is another common choice here.
 
 ``DateField``
 ~~~~~~~~~~~~~

tests/regressiontests/forms/fields.py

@@ -1077,6 +1077,53 @@ Traceback (most recent call last):
 ...
 ValidationError: [u'Select a valid choice. 6 is not one of the available choices.']
 
+# TypedChoiceField ############################################################
+
+# TypedChoiceField is just like ChoiceField, except that coerced types will 
+# be returned:
+>>> f = TypedChoiceField(choices=[(1, "+1"), (-1, "-1")], coerce=int)
+>>> f.clean('1')
+1
+>>> f.clean('2')
+Traceback (most recent call last):
+...
+ValidationError: [u'Select a valid choice. 2 is not one of the available choices.']
+
+# Different coercion, same validation.
+>>> f.coerce = float
+>>> f.clean('1')
+1.0
+
+
+# This can also cause weirdness: be careful (bool(-1) == True, remember)
+>>> f.coerce = bool
+>>> f.clean('-1') 
+True
+
+# Even more weirdness: if you have a valid choice but your coercion function
+# can't coerce, you'll still get a validation error. Don't do this!
+>>> f = TypedChoiceField(choices=[('A', 'A'), ('B', 'B')], coerce=int)
+>>> f.clean('B')
+Traceback (most recent call last):
+...
+ValidationError: [u'Select a valid choice. B is not one of the available choices.']
+
+# Required fields require values
+>>> f.clean('')
+Traceback (most recent call last):
+...
+ValidationError: [u'This field is required.']
+
+# Non-required fields aren't required
+>>> f = TypedChoiceField(choices=[(1, "+1"), (-1, "-1")], coerce=int, required=False)
+>>> f.clean('')
+''
+
+# If you want cleaning an empty value to return a different type, tell the field
+>>> f = TypedChoiceField(choices=[(1, "+1"), (-1, "-1")], coerce=int, required=False, empty_value=None)
+>>> print f.clean('')
+None
+
 # NullBooleanField ############################################################
 
 >>> f = NullBooleanField()