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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, relpath):
 """Read a file out of the repository at a certain revision. This is complicated because, unlike vanilla git cat-file, this follows symlinks in the repo. If a symlink points outside repo, the file is read from the filesystem; that's because presumably whoever put that symlink there knew what they were doing. """


    path = self._realpath(relpath)
    if path.endswith('/'):
      raise self.IsDirException(self.rev, relpath)

    if path.startswith('../') or path[0] == '/':
      yield open(path, 'rb')
      return

    object_type, data = self._read_object_from_repo(rev=self.rev, relpath=path)
    if object_type == b'tree':
      raise self.IsDirException(self.rev, relpath)
    assert object_type == b'blob'
    yield io.BytesIO(data)