Python字典的基本概念_Python自学第二十六节

>>> services = {'ftp':21,'ssh':22,'http':80}   #ftp为键，21为值
>>> services['ssh']
22
>>> services['http']
80
>>> services['http'] = 8080   #键是不能修改的，可以修改值
>>> services
{'ftp': 21, 'ssh': 22, 'http': 8080}

>>> services['https'] = 443   #增加新的元素，https之前不存在
>>> services
{'ftp': 21, 'ssh': 22, 'http': 8080, 'https': 443}
>>> services['http'] = 80   #http已经存在，则进行修改
>>> services
{'ftp': 21, 'ssh': 22, 'http': 80, 'https': 443}

>>> services.keys()
dict_keys(['ftp', 'ssh', 'http', 'https'])

>>> services.values()
dict_values([21, 22, 80, 443])

>>> services.items()
dict_items([('ftp', 21), ('ssh', 22), ('http', 80), ('https', 443)])

>>> 'http' in services   #查看是否存在'http'键
True
>>> 80 in services   #查看是否存在 80 的值，是查不到值的
False
>>> 80 in services.values()   #配合values()方法进行查看即可
True

>>> for i in services:
...     print(i)
... 
ftp
ssh
http
https

>>> for i in services:   #i取值为键
...     print(services[i])   #services[i]即可转换为字典中每个元素的值
... 
21
22
80
443
>>> for i in services.values():   #i取值直接为值
...     print(i)
... 
21
22
80
443

>>> for i in services:   #取值为键
...     print(f'{i}:{services[i]}')   #字符串格式化，f' {i}'即为键 ：{services[i]即为键的值}'
... 
ftp:21
ssh:22
http:80
https:443
方法二

>>> for m,n in services.items():   #定义两个循环变量在services.items()进行取值
...     print(f'{m}:{n}')   #字符串格式化输出如下
... 
ftp:21
ssh:22
http:80
https:443