失业程序员复习python笔记---字典和集合(1)

字典是一系列由键和值配对组成的集合

相比于列表和元组，字典的性能更优，特别是对于查找、添加和删除操作，字典都能在常数时间复杂度内完成。

集合和字典基本相同，唯一的区别，就是集合没有键和值的配对，是一系列无序的、唯一的元素组合。

字典的创建和访问方式如下：

d1 = {'name': 'regina', 'age': 20, 'gender': 'female'}
d2 = dict({'name': 'regina', 'age': 20, 'gender': 'female'})
d3 = dict([('name', 'regina'), ('age', 20), ('gender', 'female')])
d4 = dict(name='regina', age=20, gender='female')

print(d1['name'])
print(d2.get('age'))

D:\pyproject\venv\Scripts\python.exe D:/pyproject/py04.py

regina

20

Process finished with exit code 0

字典可以直接根据索引访问，如果不存在，就会直接抛异常

d1 = {'name': 'regina', 'age': 20, 'gender': 'female'}
d2 = dict({'name': 'regina', 'age': 20, 'gender': 'female'})
d3 = dict([('name', 'regina'), ('age', 20), ('gender', 'female')])
d4 = dict(name='regina', age=20, gender='female')

print(d1['name'])
print(d2['location'])

D:\pyproject\venv\Scripts\python.exe D:/pyproject/py04.py

regina

Traceback (most recent call last):

File "D:/pyproject/py04.py", line 7, in <module>

print(d2['location'])

KeyError: 'location'

Process finished with exit code 1

集合的创建和访问方式如下：

s1 = {'regina',20,'female'}
s1 = set({'regina',20,'female'})

for item in s1:
print(item)

由于集合是无序的，它们不支持索引访问。所以这样访问是要报错的

D:\pyproject\venv\Scripts\python.exe D:/pyproject/py04.py

Traceback (most recent call last):

File "D:/pyproject/py04.py", line 4, in <module>

print(s1[0])

TypeError: 'set' object is not subscriptable

Process finished with exit code 1