? 人生苦短，快學(xué)Python！

字典是否是無序的

>>>?#?Python?2.7
>>>?a_dict?=?{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}
>>>?a_dict
{'color':?'blue',?'pet':?'dog',?'fruit':?'apple'}
>>>?a_dict
{'color':?'blue',?'pet':?'dog',?'fruit':?'apple'}

>>>?#?Python?3.5
>>>?a_dict?=?{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}
>>>?a_dict
{'color':?'blue',?'pet':?'dog',?'fruit':?'apple'}
>>>?a_dict
{'color':?'blue',?'pet':?'dog',?'fruit':?'apple'}

>>>?a_dict?=?{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}
>>>?a_dict
{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}
>>>?a_dict
{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}

鍵值互換

>>>?a_dict?=?{'one':?1,?'two':?2,?'thee':?3,?'four':?4}
>>>?new_dict?=?{}
>>>?for?key,?value?in?a_dict.items():
...?????new_dict[value]?=?key
...
>>>?new_dict
{1:?'one',?2:?'two',?3:?'thee',?4:?'four'}

依據(jù)某種條件，過濾字典

>>>?a_dict?=?{'one':?1,?'two':?2,?'thee':?3,?'four':?4}
>>>?new_dict?=?{}??#?Create?a?new?empty?dictionary
>>>?for?key,?value?in?a_dict.items():
...?????if?value?<=?2:
...?????????new_dict[key]?=?value
...
>>>?new_dict
{'one':?1,?'two':?2}

利用字典中的值，做一些計算

>>>?incomes?=?{'apple':?5600.00,?'orange':?3500.00,?'banana':?5000.00}
>>>?total_income?=?0.00
>>>?for?value?in?incomes.values():
...?????total_income?+=?value??#?Accumulate?the?values?in?total_income
...
>>>?total_income
14100.0

字典推導(dǎo)式

>>>?objects?=?['blue',?'apple',?'dog']
>>>?categories?=?['color',?'fruit',?'pet']
>>>?a_dict?=?{key:?value?for?key,?value?in?zip(categories,?objects)}
>>>?a_dict
{'color':?'blue',?'fruit':?'apple',?'pet':?'dog'}

利用字典推導(dǎo)式，實現(xiàn)鍵值轉(zhuǎn)換

>>>?a_dict?=?{'one':?1,?'two':?2,?'thee':?3,?'four':?4}
>>>?new_dict?=?{value:?key?for?key,?value?in?a_dict.items()}
>>>?new_dict
{1:?'one',?2:?'two',?3:?'thee',?4:?'four'}

利用字典推導(dǎo)式，過濾字典

>>>?a_dict?=?{'one':?1,?'two':?2,?'thee':?3,?'four':?4}
>>>?new_dict?=?{k:?v?for?k,?v?in?a_dict.items()?if?v?<=?2}
>>>?new_dict
{'one':?1,?'two':?2}

利用字典推導(dǎo)式，做一些計算

>>>?incomes?=?{'apple':?5600.00,?'orange':?3500.00,?'banana':?5000.00}
>>>?total_income?=?sum([value?for?value?in?incomes.values()])
>>>?total_income
14100.0

字典排序

>>?incomes?=?{'apple':?5600.00,?'orange':?3500.00,?'banana':?5000.00}
>>>?sorted_income?=?{k:?incomes[k]?for?k?in?sorted(incomes)}
>>>?sorted_income
{'apple':?5600.0,?'banana':?5000.0,?'orange':?3500.0}

內(nèi)置函數(shù)，與字典配合使用

map()函數(shù)

>>>?prices?=?{'apple':?0.40,?'orange':?0.35,?'banana':?0.25}
>>>?def?discount(current_price):
...?????return?(current_price[0],?round(current_price[1]?*?0.95,?2))
...
>>>?new_prices?=?dict(map(discount,?prices.items()))
>>>?new_prices
{'apple':?0.38,?'orange':?0.33,?'banana':?0.24}

filter()函數(shù)

>>>?prices?=?{'apple':?0.40,?'orange':?0.35,?'banana':?0.25}
>>>?def?has_low_price(price):
...?????return?prices[price]?0.4
...
>>>?low_price?=?list(filter(has_low_price,?prices.keys()))
>>>?low_price
['orange',?'banana']

字典解包運算符

>>>?vegetable_prices?=?{'pepper':?0.20,?'onion':?0.55}
>>>?fruit_prices?=?{'apple':?0.40,?'orange':?0.35,?'pepper':?.25}
>>>?{**vegetable_prices,?**fruit_prices}
{'pepper':?0.25,?'onion':?0.55,?'apple':?0.4,?'orange':?0.35}

E?N?D