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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(self, size=None):
 """ Read `size` of bytes."""

    if size is None:
      return self.buf.read() + self.open_file.read()
    contents = self.buf.read(size)
    if len(contents) < size:
      contents += self.open_file.read(size - len(contents))
    return contents