<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def country_code_for_valid_region(region_code):
 """Returns the country calling code for a specific region. For example, this would be 1 for the United States, and 64 for New Zealand. Assumes the region is already valid. Arguments: region_code -- The region that we want to get the country calling code for. Returns the country calling code for the region denoted by region_code. """

    metadata = PhoneMetadata.metadata_for_region(region_code.upper(), None)
    if metadata is None:
        raise Exception("Invalid region code %s" % region_code)
    return metadata.country_code