11个好用到起飞的「Python字典」知识点！
人生苦短，快学Python！
字典这个概念，将会伴随着你后面的学习和工作。字典是否是无序的
>>> # 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'}
键值互换
>>> 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'}
依据某种条件，过滤字典
>>> 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，做一些计算
>>> 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
字典推导式
>>> 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'}
利用字典推导式，实现键值转换
>>> 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'}
利用字典推导式，过滤字典
>>> 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}
利用字典推导式，做一些计算
>>> 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}
内置函数，与字典配合使用
map()函数
>>> 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()函数
>>> 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']
字典解包运算符
>>> 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}
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