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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 _find_best_fit(self, pbin):
 """ Return best fitness rectangle from rectangles packing _sorted_rect list Arguments: pbin (PackingAlgorithm):
 Packing bin Returns: key of the rectangle with best fitness """

        fit = ((pbin.fitness(r[0], r[1]), k) for k, r in self._sorted_rect.items())
        fit = (f for f in fit if f[0] is not None)
        try:
            _, rect = min(fit, key=self.first_item)
            return rect
        except ValueError:
            return None