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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 _region_from_key_id(key_id, default_region=None):
 """Determine the target region from a key ID, falling back to a default region if provided. :param str key_id: AWS KMS key ID :param str default_region: Region to use if no region found in key_id :returns: region name :rtype: str :raises UnknownRegionError: if no region found in key_id and no default_region provided """

    try:
        region_name = key_id.split(":", 4)[3]
    except IndexError:
        if default_region is None:
            raise UnknownRegionError(
                "No default region found and no region determinable from key id: {}".format(key_id)
            )
        region_name = default_region
    return region_name