Ticket #4386: newforms-cleanmethod.diff

docs/newforms.txt

@@ -301 +301 @@
 empty values as an empty string. Each field type knows what its "blank" value
 is -- e.g., for ``DateField``, it's ``None`` instead of the empty string.
 
+Custom Validation and Cleaning:
+-------------------------------
+
+You can write custom validation methods. The method must be called
+``clean_FIELDNAME``. It is possible to alter the value, too. Example:
+
+    >>> class OptionalPersonForm(Form):
+    ...     first_name = CharField()
+    ...     def clean_first_name(self):
+    ...         value = self.fields["first_name"].widget.value_from_datadict(self.data, self.add_prefix("first_name"))
+    ...         if not re.match(r'^[a-zA-Z]+$', value):
+    ...             raise ValidationError("Only a-z A-Z allowed.")
+    ...         return value
+
+
 Behavior of unbound forms
 ~~~~~~~~~~~~~~~~~~~~~~~~~