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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 open(self, filename):
 """ Yield a file-like object for file `filename`. This function is a context manager. """

        filename = self.real_filename(filename)

        if not os.path.exists(filename):
            raise self.FileNotFound(filename)

        with codecs.open(filename, encoding='utf-8') as f:
            yield f