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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_identifier(self, idx):
 """Return an identifier for the data at index `idx` .. versionchanged:: 0.4.2 indexing starts at 1 instead of 0 """

        name = self._get_cropped_file_names()[idx]
        return "{}:{}:{}".format(self.identifier, name, idx + 1)