Python: 字典dict: zip()

problem: 怎样在数据字典中执行一些计算操做(好比求最小值、最大值、排序等等)？

answer：

    eg1:

 

                考虑下面的股票名和价格映射字典：

                　　prices = {'ACME': 45.23,'AAPL': 612.78,'IBM': 205.55,'HPQ': 37.20,'FB': 10.75}

                  为了对字典值执行计算操做,一般须要使用zip()函数先将键和值反转过来.下面是查找最小和最大股票价格和股票值的代码：

　　　　　　　 min_price = min(zip(prices.values(), prices.keys()))
                          # min_price is (10.75, 'FB')
                          max_price = max(zip(prices.values(), prices.keys()))
                          # max_price is (612.78, 'AAPL')

                  相似的，能够使用zip() 和sorted() 函数来排列字典数据：

                        prices_sorted = sorted(zip(prices.values(), prices.keys()))
                        # prices_sorted is [(10.75, 'FB'), (37.2, 'HPQ'),
                        # (45.23, 'ACME'), (205.55, 'IBM'),
                        # (612.78, 'AAPL')]

 

                  执行这些计算的时候，须要注意的是zip() 函数建立的是一个只能访问一次的迭代器。好比，下面的代码就会产生错误：

                           prices_and_names = zip(prices.values(), prices.keys())
                           print(min(prices_and_names)) # OK
                           print(max(prices_and_names)) # ValueError: max() arg is an empty sequence

    eg2:

 

               字典值相同，键不一样，比较值的大小

                    >>> prices = { 'AAA' : 45.23, 'ZZZ': 45.23 }
                    >>> min(zip(prices.values(), prices.keys()))
                    (45.23, 'AAA')
                   >>> max(zip(prices.values(), prices.keys()))
                   (45.23, 'ZZZ')