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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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:Python27python.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