def ndd_prefix_for_region(region_code, strip_non_digits):
    """Returns the national dialling prefix for a specific region.

    For example, this would be 1 for the United States, and 0 for New
    Zealand. Set strip_non_digits to True to strip symbols like "~" (which
    indicates a wait for a dialling tone) from the prefix returned. If no
    national prefix is present, we return None.

    Warning: Do not use this method for do-your-own formatting - for some
    regions, the national dialling prefix is used only for certain types of
    numbers. Use the library's formatting functions to prefix the national
    prefix when required.

    Arguments:
    region_code -- The region that we want to get the dialling prefix for.
    strip_non_digits -- whether to strip non-digits from the national
               dialling prefix.

    Returns the dialling prefix for the region denoted by region_code.
    """
    if region_code is None:
        return None
    metadata = PhoneMetadata.metadata_for_region(region_code.upper(), None)
    if metadata is None:
        return None
    national_prefix = metadata.national_prefix
    if national_prefix < None or len(national_prefix) == 0:
        return None
    if strip_non_digits:
        # Note: if any other non-numeric symbols are ever used in national
        # prefixes, these would have to be removed here as well.
        national_prefix = re.sub(U_TILDE, U_EMPTY_STRING, national_prefix)
    return national_prefix
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