字典一种key - value 的数据类型。
字典是无序的，键必须是唯一的，但值则不必，值可以取任何数据类型，但键必须是不可变的，如字符串，数字或元组。
字典的常用操作
创建
直接创建
dict1 = {‘student1‘:‘01‘,‘color‘:[‘red‘,‘white‘],‘guangdong‘:{‘guangzhou‘:[‘haizhu‘,‘tianhe‘],‘shenzhen‘:[‘nanshan‘,‘futian‘]}}
通过dict函数创建
#通过list创建
>>> student = [(‘student1‘,‘01‘),(‘student2‘,‘02‘)]
>>> student_dict = dict(student)
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘}
#通过关键字参数创建
>>> student_dict = dict(student1=‘01‘,student2=‘02‘,student3=‘03‘)
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘}
追加
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘}
>>> student_dict[‘student4‘] = ‘04‘
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘}
修改
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘}
>>> student_dict[‘student4‘] = ‘004‘
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘004‘}
删除
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘004‘}
>>> student_dict.pop(‘student4‘)
‘004‘
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘}
>>> del student_dict[‘student3‘]
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘}
>>> student_dict.popitem() #随机删除
(‘student2‘, ‘02‘)
>>> student_dict
{‘student1‘: ‘01‘}
查找
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘}
>>> ‘student1‘ in student_dict
True
>>> student_dict.get(‘student1‘)
‘01‘
>>> student_dict[‘student1‘]
‘01‘
>>> student_dict.get(‘student5‘)
>>> student_dict[‘student5‘] #如果一个key不存在，就报错，get方法不会，不存在只返回None
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘}
>>> student_dict.keys()
dict_keys([‘student1‘, ‘student2‘, ‘student3‘, ‘student4‘])
>>> student_dict.values()
dict_values([‘01‘, ‘02‘, ‘03‘, ‘04‘])
>>> student_dict.items()
dict_items([(‘student1‘, ‘01‘), (‘student2‘, ‘02‘), (‘student3‘, ‘03‘), (‘student4‘, ‘04‘)])
>>> type(student_dict.items())
<class ‘dict_items‘>
>>> type(student_dict)
<class ‘dict‘>
#嵌套字典查找
>>> dict1 = {‘student1‘:‘01‘,‘color‘:[‘red‘,‘white‘],‘guangdong‘:{‘guangzhou‘:[‘haizhu‘,‘tianhe‘],‘shenzhen‘:[‘nanshan‘,‘futian‘]}}
>>> dict1[‘guangdong‘][‘guangzhou‘][0]
‘haizhu‘
更新
>>> student_dict2 = {‘student5‘:‘05‘,‘student2‘:‘002‘}
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘02‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘}
>>> student_dict.update(student_dict2) #用字典student_dict2更新，更新键对应的新值，添加新的键值对。
>>> student_dict
{‘student1‘: ‘01‘, ‘student2‘: ‘002‘, ‘student3‘: ‘03‘, ‘student4‘: ‘04‘, ‘student5‘: ‘05‘}
遍历
#方法1
for key in info:
print(key,info[key])
#方法2
for k,v in info.items(): #会先把dict转成list,数据大时尽量不要用
print(k,v)
字典相关的函数
| 序号 | 函数及描述 | 实例 |
|---|---|---|
| 1 | len(dict) 计算字典元素个数，即键的总数。 |
>>> dict = {‘Name‘: ‘Runoob‘, ‘Age‘: 7, ‘Class‘: ‘First‘}
>>> len(dict)
3
|
| 2 | str(dict) 输出字典，以可打印的字符串表示。 |
>>> dict = {‘Name‘: ‘Runoob‘, ‘Age‘: 7, ‘Class‘: ‘First‘}
>>> str(dict)
"{‘Name‘: ‘Runoob‘, ‘Class‘: ‘First‘, ‘Age‘: 7}"
|
| 3 | type(variable) 返回输入的变量类型，如果变量是字典就返回字典类型。 |
>>> dict = {‘Name‘: ‘Runoob‘, ‘Age‘: 7, ‘Class‘: ‘First‘}
>>> type(dict)
<class ‘dict‘>
|
字典的内置方法
| 序号 | 函数及描述 |
|---|---|
| 1 | radiansdict.clear() 删除字典内所有元素 |
| 2 | radiansdict.copy() 返回一个字典的浅复制 |
| 3 | radiansdict.fromkeys() 创建一个新字典，以序列seq中元素做字典的键，val为字典所有键对应的初始值 |
| 4 | radiansdict.get(key, default=None) 返回指定键的值，如果值不在字典中返回default值 |
| 5 | key in dict 如果键在字典dict里返回true，否则返回false |
| 6 | radiansdict.items() 以列表返回可遍历的(键, 值) 元组数组 |
| 7 | radiansdict.keys() 以列表返回一个字典所有的键 |
| 8 | radiansdict.setdefault(key, default=None) 和get()类似, 但如果键不存在于字典中，将会添加键并将值设为default |
| 9 | radiansdict.update(dict2) 把字典dict2的键/值对更新到dict里 |
| 10 | radiansdict.values() 以列表返回字典中的所有值 |
| 11 | pop(key[,default]) 删除字典给定键 key 所对应的值，返回值为被删除的值。key值必须给出。 否则，返回default值。 |
| 12 | popitem() 随机返回并删除字典中的一对键和值(一般删除末尾对)。 |
参考链接：http://www.runoob.com/python3/python3-dictionary.html
参考链接：http://www.cnblogs.com/alex3714/articles/5717620.html
