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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_field_name(self, field):
 """ Returns the field name for a given field. """

        for field_name, f in self.fields.items():
            if f == field:
                return field_name
        raise AttributeError("Field %s does not exists in %s resource" % (
            field, self.__class__))