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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 _cells(nb):
 """Yield all cells in an nbformat-insensitive manner"""

    if nb.nbformat < 4:
        for ws in nb.worksheets:
            for cell in ws.cells:
                yield cell
    else:
        for cell in nb.cells:
            yield cell