def checkDockerImageExists(appliance):
    """
    Attempts to check a url registryName for the existence of a docker image with a given tag.

    :param str appliance: The url of a docker image's registry (with a tag) of the form:
                          'quay.io/<repo_path>:<tag>' or '<repo_path>:<tag>'.
                          Examples: 'quay.io/ucsc_cgl/toil:latest', 'ubuntu:latest', or
                          'broadinstitute/genomes-in-the-cloud:2.0.0'.
    :return: Raises an exception if the docker image cannot be found or is invalid.  Otherwise, it
             will return the appliance string.
    :rtype: str
    """
    if currentCommit in appliance:
        return appliance
    registryName, imageName, tag = parseDockerAppliance(appliance)

    if registryName == 'docker.io':
        return requestCheckDockerIo(origAppliance=appliance, imageName=imageName, tag=tag)
    else:
        return requestCheckRegularDocker(origAppliance=appliance, registryName=registryName, imageName=imageName, tag=tag)
def checkDockerImageExists ( appliance ) : if currentCommit in appliance : return appliance registryName , imageName , tag = parseDockerAppliance ( appliance ) if registryName == 'docker.io' : return requestCheckDockerIo ( origAppliance = appliance , imageName = imageName , tag = tag ) else : return requestCheckRegularDocker ( origAppliance = appliance , registryName = registryName , imageName = imageName , tag = tag )
Attempts to check a url registryName for the existence of a docker image with a given tag.

    :param str appliance: The url of a docker image's registry (with a tag) of the form:
                          'quay.io/<repo_path>:<tag>' or '<repo_path>:<tag>'.
                          Examples: 'quay.io/ucsc_cgl/toil:latest', 'ubuntu:latest', or
                          'broadinstitute/genomes-in-the-cloud:2.0.0'.
    :return: Raises an exception if the docker image cannot be found or is invalid.  Otherwise, it
             will return the appliance string.
    :rtype: str