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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 _read_country_names(self, countries_file=None):
 """Read list of countries from specified country file or default file."""

        if not countries_file:
            countries_file = os.path.join(os.path.dirname(__file__), self.COUNTRY_FILE_DEFAULT)
        with open(countries_file) as f:
            countries_json = f.read()

        return json.loads(countries_json)