Python 数据类型-3

字典 （dict）

Python中唯一的映射的类型（哈希表）
字典对象是可变的，但是字典的键必须使用不可变的对象，一个字典可以使用不同类型的键值

定义字典：

In [68]: dic = {}   #使用 ｛｝创建空字典
In [69]: dic
Out[69]: {}
In [70]: type(dic)
Out[70]: dict

In [71]: dic = {'a':1, 1:'abc'}   #使用 ｛｝ 创建字典
In [72]: dic
Out[72]: {1: 'abc', 'a': 1}   #无序
In [73]: type(dic)
Out[73]: dict

In [77]: list1 = ['name', 'age'] #将列表合并为字典
In [78]: list2 = ['tom', 20]
In [79]: dict(zip(list1, list2))  #dict（）函数创建字典
Out[79]: {'age': 20, 'name': 'tom'}


In [81]: dict(x=10,y=11)   ##使用dict()函数创建字典
Out[81]: {'x': 10, 'y': 11}
 
In [82]: dict.fromkeys('abce',100) ##使用dict.fromkeys（）方法创建字典
Out[82]: {'a': 100, 'b': 100, 'c': 100, 'e': 100}

方法：

get() 根据键获取值

k = {"name":"lijunjiang", "age":20}

print(k.get("name"))
print(k.get("age"))
print(k.get("address"))
执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
lijunjiang
20
None  #没有的键值返回 None

Process finished with exit code 0

setdefault() 设置默认值,当KEY有值时,保持原值,当key没有值则设置该key的值

k = {"name":"lijunjiang", "age":20}
print(k.setdefault("name", "libai"))
print(k.setdefault("age", 19))
print(k.setdefault("address", "beijing"))

print(k)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
lijunjiang
20
beijing
{'age': 20, 'name': 'lijunjiang', 'address': 'beijing'}

Process finished with exit code 0

keys() 获的字典的Key (一次性取出所有)

iterkeys() 获得一个对象 (逐个取出) 效率高

k = {"name":"lijunjiang", "age":20}

print(k.keys())

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
['age', 'name']

Process finished with exit code 0

values() 获取所有key的值(一次性取出所有)
iteritems() 获得一个对象(逐个取出) 效率高

k = {"name":"lijunjiang", "age":20}

print(k.values())

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
[20, 'lijunjiang']

Process finished with exit code 0

iterkey iteritems items(逐个将key:values取出返回一个列表)

k = {"name":"lijunjiang", "age":20}

for x, y in k.iteritems():
    print( x , y)

print(k.items())
执行:

C:\Python27\python.exe D:/Python/type-of-data1.py
('age', 20)
('name', 'lijunjiang')
[('age', 20), ('name', 'lijunjiang')]

Process finished with exit code 0

pop() 删除某个在的键值,必须输入一个存在的key,否则会报错

k = {"name":"lijunjiang", "age":20}
k.setdefault("addr", "beijing")
print(k)

k.pop("name")
print(k)
k.pop("addr")
print(k)


执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
{'age': 20, 'name': 'lijunjiang', 'addr': 'beijing'}
{'age': 20, 'addr': 'beijing'}
{'age': 20}

Process finished with exit code 0

fromkeys()

list1 = ["a", "b", "c", "d"]
k = {}
n = k.fromkeys(list1, 123)
print(n)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
{'a': 123, 'c': 123, 'b': 123, 'd': 123}

Process finished with exit code 0

zip()

list1 = ["a", "b", "c", "d"]
list2 = [12, 234, 32, 23]
n = zip(list1, list2)
print(n)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
[('a', 12), ('b', 234), ('c', 32), ('d', 23)]

Process finished with exit code 0

#########################################################33

dict() 

列表转换成字典

list1 = ["a", "b", "c", "d"]
list2 = [12, 234, 32, 23]
n = dict(zip(list1, list2))
print(n)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
{'a': 12, 'c': 32, 'b': 234, 'd': 23}

Process finished with exit code 0

dict.updata()

list1 = ["a", "b", "c", "d"]
list2 = [12, 234, 32, 23]
n = dict(zip(list1, list2))
print(n)

k = {"name": "lijunjiang", "age": 20}

k.update(n)
print(k)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
{'a': 12, 'c': 32, 'b': 234, 'd': 23}
{'a': 12, 'c': 32, 'b': 234, 'name': 'lijunjiang', 'age': 20, 'd': 23}

Process finished with exit code 0

sorted()

mm = dict(a=1, b=120, c=5, d=50)
print sorted(mm.iteritems(), key = lambda d: d[1], reverse=True)
print sorted(mm.iteritems(), key = lambda a: a[0], reverse=True)

执行:
C:\Python27\python.exe D:/Python/type-of-data1.py
[('b', 120), ('d', 50), ('c', 5), ('a', 1)]
[('d', 50), ('c', 5), ('b', 120), ('a', 1)]

Process finished with exit code 0