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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 pstdev(data, mu=None):
 """Return the square root of the population variance. See ``pvariance`` for arguments and other details. """

    var = pvariance(data, mu)
    try:
        return var.sqrt()
    except AttributeError:
        return math.sqrt(var)