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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 get_placeholder_cache_key_for_parent(parent_object, placeholder_name, language_code):
 """ Return a cache key for a placeholder. This key is used to cache the entire output of a placeholder. """

    parent_type = ContentType.objects.get_for_model(parent_object)
    return _get_placeholder_cache_key_for_id(
        parent_type.id,
        parent_object.pk,
        placeholder_name,
        language_code
    )