From 6c984587711f82c0fc5223bbf6e8bb3b71732a3e Mon Sep 17 00:00:00 2001 From: Tim Graham Date: Fri, 5 Jul 2013 06:53:19 -0400 Subject: [PATCH] [1.5.x] Fixed #19539 -- Updated custom model fields example for Python 3. Thanks astorije@ for the report. Backport of b9fceadfd4 from master. --- docs/howto/custom-model-fields.txt | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/docs/howto/custom-model-fields.txt b/docs/howto/custom-model-fields.txt index 7d9dc8bc8b..54f2da7a1d 100644 --- a/docs/howto/custom-model-fields.txt +++ b/docs/howto/custom-model-fields.txt @@ -249,7 +249,7 @@ appropriate Python object. The details of how this happens internally are a little complex, but the code you need to write in your ``Field`` class is simple: make sure your field subclass uses a special metaclass: -For example:: +For example, on Python 2:: class HandField(models.Field): @@ -258,7 +258,21 @@ For example:: __metaclass__ = models.SubfieldBase def __init__(self, *args, **kwargs): - # ... + ... + +On Python 3, in lieu of setting the ``__metaclass__`` attribute, add +``metaclass`` to the class definition:: + + class HandField(models.Field, metaclass=models.SubfieldBase): + ... + +If you want your code to work on Python 2 & 3, you can use +:func:`six.with_metaclass`:: + + from django.utils.six import with_metaclass + + class HandField(with_metaclass(models.SubfieldBase, models.Field)): + ... This ensures that the :meth:`.to_python` method, documented below, will always be called when the attribute is initialized.