gistfile1.py

import pickle


class FieldTracker(object):
    def patch_save(self, instance):
        original_save = instance.save

        def save(**kwargs):
            ret = original_save(**kwargs)

            # use properties of self, implement new stuff etc
            print 'Used patched save'

            return ret

        instance.save = save


class Model(object):
    name_field = 'joe'

    field_tracker = FieldTracker()

    def __init__(self):
        self.field_tracker.patch_save(self)

    def save(self):
        print 'Used default save'

model = Model()
model.save()  # Uses patched version of save

pickle.dumps(model)  # Fails