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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def object_version_choices(obj):
 """ Return a list of form choices for versions of this object which can be published. """

    choices = BLANK_CHOICE_DASH + [(PublishAction.UNPUBLISH_CHOICE, 'Unpublish current version')]

    # When creating a new object in the Django admin - obj will be None
    if obj is not None:
        saved_versions = Version.objects.filter(
            content_type=ContentType.objects.get_for_model(obj),
            object_id=obj.pk,
        ).exclude(
            version_number=None,
        )

        for version in saved_versions:
            choices.append((version.version_number, version))

    return choices