Fixed django#19639 - Updated contributing to reflect model choices best practices.

Thanks charettes.

Author: timgraham

docs/internals/contributing/writing-code/coding-style.txt

@@ -136,14 +136,17 @@ Model style
  * ``def get_absolute_url()``
  * Any custom methods
 
-* If ``choices`` is defined for a given model field, define the choices as
- a tuple of tuples, with an all-uppercase name, either near the top of
- the model module or just above the model class. Example::
-
- DIRECTION_CHOICES = (
- ('U', 'Up'),
- ('D', 'Down'),
- )
+* If ``choices`` is defined for a given model field, define each choice as
+ a tuple of tuples, with an all-uppercase name as a class attribute on the
+ model. Example::
+
+ class MyModel(models.Model):
+ DIRECTION_UP = 'U'
+ DIRECTION_DOWN = 'D'
+ DIRECTION_CHOICES = (
+ (DIRECTION_UP, 'Up'),
+ (DIRECTION_DOWN, 'Down'),
+ )
 
 Use of ``django.conf.settings``
 -------------------------------