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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 push_images():
 # type: () -> None """ Push all project docker images to a remote registry. """

    registry = conf.get('docker.registry')
    docker_images = conf.get('docker.images', [])

    if registry is None:
        log.err("You must define docker.registry conf variable to push images")
        sys.exit(-1)

    for image in docker_images:
        push_image(registry, image)