problem: 怎樣在數據字典中執行一些計算操做(好比求最小值、最大值、排序等等)?函數
answer:spa
eg1:排序
考慮下面的股票名和價格映射字典:ip
prices = {'ACME': 45.23,'AAPL': 612.78,'IBM': 205.55,'HPQ': 37.20,'FB': 10.75}數據
爲了對字典值執行計算操做,一般須要使用zip()函數先將鍵和值反轉過來.下面是查找最小和最大股票價格和股票值的代碼:sort
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')co
相似的,能夠使用zip() 和sorted() 函數來排列字典數據:字典
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')]background
執行這些計算的時候,須要注意的是zip() 函數建立的是一個只能訪問一次的迭代器。好比,下面的代碼就會產生錯誤:錯誤
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,鍵不一樣,比較值的大小
>>> 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')