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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 get_validator(self, schema=None):
 """Get a jsonschema validator. :param dict schema: A custom schema to validate against. :returns: an instance of jsonschema Draft4Validator. """

        schema = schema if schema is not None else self.schema
        return jsonschema.Draft4Validator(
            schema, resolver=self.resolver,
            format_checker=jsonschema.draft4_format_checker)