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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_code_for_short_number_from_region_list(numobj, region_codes):
 """Helper method to get the region code for a given phone number, from a list of possible region codes. If the list contains more than one region, the first region for which the number is valid is returned. """

    if len(region_codes) == 0:
        return None
    elif len(region_codes) == 1:
        return region_codes[0]
    national_number = national_significant_number(numobj)
    for region_code in region_codes:
        metadata = PhoneMetadata.short_metadata_for_region(region_code)
        if metadata is not None and _matches_possible_number_and_national_number(national_number, metadata.short_code):
            # The number is valid for this region.
            return region_code
    return None