add new forms example

mattmakai · mattmakai · commit 518295869d90 · 2019-06-16T16:45:05.000-04:00
diff --git a/content/pages/examples/django/django-forms.markdown b/content/pages/examples/django/django-forms.markdown
@@ -611,6 +611,7 @@ class SetPasswordField(PasswordField):
 # source file continues from here with a few more good forms examples
 ```
 
+
 ## Example 3 from heritagesites
 [heritagesites](https://github.com/Michael-Cantley/heritagesites) is a
 [Django](/django.html) web application with a [MySQL](/mysql.html)
@@ -640,3 +641,96 @@ from heritagesites.models import HeritageSite
 ~~        self.helper.form_method = 'post'
 ~~        self.helper.add_input(Submit('submit', 'submit'))
 ```
+
+
+## Example 4 from edX
+[edX](https://github.com/edx)
+([project website](https://open.edx.org/))
+is an open source platform for teaching online courses that is widely
+used in academia and industry. The platform code is available under the 
+[GNU Affero General Public License v3.0](https://github.com/edx/edx-platform/blob/master/LICENSE).
+
+[**edx-platform/openedx/core/djangoapps/util/forms.py**]("https://github.com/edx/edx-platform/blob/master/openedx/core/djangoapps/util/forms.py)
+
+```python
+from __future__ import absolute_import
+
+from django.core.exceptions import ValidationError
+~~from django.forms import Field, MultipleHiddenInput, NullBooleanField, Select
+
+
+~~class MultiValueField(Field):
+    """
+    Field class that supports a set of values for a single form field.
+    The field input can be specified as:
+        1. a comma-separated-list (foo:bar1,bar2,bar3), or
+        2. a repeated field in a MultiValueDict (foo:bar1, foo:bar2, foo:bar3)
+        3. a combination of the above (foo:bar1,bar2, foo:bar3)
+    Note that there is currently no way to pass a value that includes a comma.
+    The resulting field value is a python set of the values as strings.
+    """
+~~    widget = MultipleHiddenInput
+
+~~    def to_python(self, list_of_string_values):
+        """
+        Convert the form input to a list of strings
+        """
+~~        values = super(MultiValueField, self).to_python(list_of_string_values) or set()
+
+~~        if values:
+            # combine all values if there were multiple specified individually
+~~            values = ','.join(values)
+
+            # parse them into a set
+~~            values = set(values.split(',')) if values else set()
+
+~~        return values
+
+~~    def validate(self, values):
+        """
+        Ensure no empty values were passed
+        """
+~~        if values and "" in values:
+~~            raise ValidationError("This field cannot be empty.")
+
+
+~~class ExtendedNullBooleanField(NullBooleanField):
+    """
+    A field whose valid values are None, True, 'True', 'true', '1',
+    False, 'False', 'false' and '0'.
+    """
+
+    NULL_BOOLEAN_CHOICES = (
+        (None, ""),
+        (True, True),
+        (True, "True"),
+        (True, "true"),
+        (True, "1"),
+        (False, False),
+        (False, "False"),
+        (False, "false"),
+        (False, "0"),
+    )
+
+~~    widget = Select(choices=NULL_BOOLEAN_CHOICES)
+
+~~    def to_python(self, value):
+~~        return to_bool(value)
+
+
+def to_bool(value):
+    """
+    Explicitly checks for the string 'True', 'False', 'true',
+    'false', '1' and '0' and returns boolean True or False.
+    Returns None if value is not passed at all and raises an
+    exception for any other value.
+    """
+    if value in (True, 'True', 'true', '1'):
+        return True
+    elif value in (False, 'False', 'false', '0'):
+        return False
+    elif not value:
+        return None
+    else:
+        raise ValidationError("Invalid Boolean Value.")
+```
