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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 set_ocha_url(cls, url=None):
 # type: (str) -> None """ Set World Bank url from which to retrieve countries data Args: url (str):
 World Bank url from which to retrieve countries data. Defaults to internal value. Returns: None """

        if url is None:
            url = cls._ochaurl_int
        cls._ochaurl = url