组合数据类型（字典）

1，创建字典

a，直接创建

dic = {'a':1,'b':2,'c':3}                
print (dic)
>>>{'b': 2, 'a': 1, 'c': 3}

　　b，函数创建

dic= dict(a=1,b=2,c=3)            
print (dic)
>>>{'b': 2, 'c': 3, 'a': 1}　

2，基本操作

a，判断

dic1 = {'a':1,'b':2,'c':3} 
print ('a' in dic1)           # 此处只能判断key
print (1 in dic1)
>>>True
False

b，追加

dic = {'a':1,'b':2,'c':3} 
dic['d'] = 4
print (dic)
>>>{'c': 3, 'a': 1, 'b': 2, 'd': 4}

　　c，修改

dic = {'a':1,'b':2,'c':3} 
dic['a'] = 4
print (dic)
>>>{'c': 3, 'a': 4, 'b': 2}

　　d，删除

dic = {'a':1,'b':2,'c':3} 
del dic['a']
print (dic)
>>>{'c': 3, 'b': 2}　　

3，常用功能

a，追加

dic1 = {'a':1,'b':2,'c':3} 
dic2 = {'d':4}
dic3 = dic2.update(dic1)           # 将字典dic1合并到字典dic2中去
print (dic1)
print (dic2)
>>>{'b': 2, 'a': 1, 'c': 3}
{'d': 4, 'a': 1, 'b': 2, 'c': 3}

　　c，复制

dic1 = {'a':1,'b':2,'c':3} 
dic2 = {'d':4}
dic3 = dic1.copy()
dic1.update(dic2)    # 注意不能将追加后的字典直接赋值给变量dic4=dic1.update(dic2)    
print (dic3)
print (dic1)

d，清空

dic = {'a':1,'b':2,'c':3} 
dic.clear()             # 清空字典
print (dic)
>>>{}

4，访问字典

a，获取健key对应值value

dic = {'a':1,'b':2,'c':3} 
print (dic.get('a'))
>>>1

b，获取所有健key

dic = {'a':1,'b':2,'c':3} 
print (dic.keys())
>>>dict_keys(['a', 'b', 'c'])

c，获取所有值value

dic = {'a':1,'b':2,'c':3} 
print (dic.values()
>>>dict_values([1, 2, 3])

d，获取健值对items

dic = {'a':1,'b':2,'c':3} 
print (dic.items())
>>>dict_items([('a', 1), ('b', 2), ('c', 3)])

5，遍历字典

a，遍历所有健key

dic = {'a':1,'b':2,'c':3} 
for key in dic.keys():
    print (key)
>>>b
a
c　

　　b，遍历所有值values

dic = {'a':1,'b':2,'c':3} 
for value in dic.values():
    print (value)
>>>2
1
3

　　c，遍历所有健值对items

dic = {'a':1,'b':2,'c':3} 
for (k,v) in dic.items():
    print (k,v)
>>>a 1
b 2
c 3