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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 _update_pdf(population, fitnesses, pdfs, quantile):
 """Find a better pdf, based on fitnesses."""

    # First we determine a fitness threshold based on a quantile of fitnesses
    fitness_threshold = _get_quantile_cutoff(fitnesses, quantile)

    # Then check all of our possible pdfs with a stochastic program
    return _best_pdf(pdfs, population, fitnesses, fitness_threshold)