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diff --git a/lib/python2.7/site-packages/django/db/models/fields/subclassing.py b/lib/python2.7/site-packages/django/db/models/fields/subclassing.py
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index 0000000..e6153ae
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+++ b/lib/python2.7/site-packages/django/db/models/fields/subclassing.py
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+"""
+Convenience routines for creating non-trivial Field subclasses, as well as
+backwards compatibility utilities.
+
+Add SubfieldBase as the metaclass for your Field subclass, implement
+to_python() and the other necessary methods and everything will work
+seamlessly.
+"""
+
+class SubfieldBase(type):
+    """
+    A metaclass for custom Field subclasses. This ensures the model's attribute
+    has the descriptor protocol attached to it.
+    """
+    def __new__(cls, name, bases, attrs):
+        new_class = super(SubfieldBase, cls).__new__(cls, name, bases, attrs)
+        new_class.contribute_to_class = make_contrib(
+            new_class, attrs.get('contribute_to_class')
+        )
+        return new_class
+
+class Creator(object):
+    """
+    A placeholder class that provides a way to set the attribute on the model.
+    """
+    def __init__(self, field):
+        self.field = field
+
+    def __get__(self, obj, type=None):
+        if obj is None:
+            raise AttributeError('Can only be accessed via an instance.')
+        return obj.__dict__[self.field.name]
+
+    def __set__(self, obj, value):
+        obj.__dict__[self.field.name] = self.field.to_python(value)
+
+def make_contrib(superclass, func=None):
+    """
+    Returns a suitable contribute_to_class() method for the Field subclass.
+
+    If 'func' is passed in, it is the existing contribute_to_class() method on
+    the subclass and it is called before anything else. It is assumed in this
+    case that the existing contribute_to_class() calls all the necessary
+    superclass methods.
+    """
+    def contribute_to_class(self, cls, name):
+        if func:
+            func(self, cls, name)
+        else:
+            super(superclass, self).contribute_to_class(cls, name)
+        setattr(cls, self.name, Creator(self))
+
+    return contribute_to_class