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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_signer_hostname():
 """ Returns the IOpipe signer hostname for a region :returns: The signer hostname :rtype str """

    region = os.getenv("AWS_REGION", "")
    region = region if region and region in SUPPORTED_REGIONS else "us-west-2"
    return "signer.{region}.iopipe.com".format(region=region)