Python3基础之字典

Python数据类型之字典(Dictionary)

字典特征

1. 特征
   可变、无序、映射、键值对
2. 形式
   {key0:value0, key1:value1, key2:value3, ..., }

key：唯一性，key的数据类型必须是固定不可变的，如数字、字符串、元组、冻结集合

value：任意python数据类型

创建字典容器对象

my_study = {'数学':'math is a kind of art', '语文':'writing', '外语':'communication'}
print(my_study)
{'数学': 'math is a kind of art', '语文': 'writing', '外语': 'communication'}

my_character = {1:'beauty', 2:'handsome', 3:'happy', 4:'good'}
print(my_character)
{1: 'beauty', 2: 'handsome', 3: 'happy', 4: 'good'}

my_test = {(1,2):12, (3,4):34, (4,5):56}
print(my_test)
{(1, 2): 12, (3, 4): 34, (4, 5): 56}

my_test_temp = {'a':66, 1:'1', (0,0):[1,2,3], ('a','b'):{'1':1,'2':2}}
print(my_test_temp)
{'a': 66, 1: '1', (0, 0): [1, 2, 3], ('a', 'b'): {'1': 1, '2': 2}}

my_good_dict = {frozenset({1,2,3}):123, frozenset({4,5,6}):456}
print(my_good_dict)
{frozenset({1, 2, 3}): 123, frozenset({4, 5, 6}): 456}

字典的常见操作

• 向字典中添加元素

I_dict = {1:'1', 2:'2', 3:'3'}
I_dict[4] = '4'  # 添加4:'4'这个键值对
print(I_dict)
{1: '1', 2: '2', 3: '3', 4: '4'}

I_dict.setdefault('My_add')   # 添加 'My_add':None这个键值对
print(I_dict)
{1: '1', 2: '2', 3: '3', 4: '4', 'My_add': None}

I_dict.setdefault(5,'5')  # 添加5:'5'这个键值对，返回'5'
print(I_dict)
{1: '1', 2: '2', 3: '3', 4: '4', 'My_add': None, 5: '5'}

I_dict_1 = {'a':1,'b':2,'c':3, 1:'a'}
I_dict.update(I_dict_1)  # 用I_dict_1更新当前字典，key值重复的采用更新的值替换
I_dict
{1: 'a',
2: '2',
3: '3',
4: '4',
'My_add': None,
5: '5',
'a': 1,
'b': 2,
'c': 3}

• 查找字典元素

dict_temp = {'1':1,'2':2,'3':3,'4':4,'a':[1,2,3],'b':(1,2,3)}

print(dict_temp['a'])
[1, 2, 3]

print(dict_temp.get('2'))
2

print(dict_temp.keys())
dict_keys(['1', '2', '3', '4', 'a', 'b'])

print(dict_temp.values())
dict_values([1, 2, 3, 4, [1, 2, 3], (1, 2, 3)])

print(dict_temp.items())
dict_items([('1', 1), ('2', 2), ('3', 3), ('4', 4), ('a', [1, 2, 3]), ('b', (1, 2, 3))])

• 字典的元素删除操作

keys = list(range(4))
values = [x for x in 'abcd']
dict_ = dict(zip(keys, values))
dict_
{0: 'a', 1: 'b', 2: 'c', 3: 'd'}

dict_.pop(2) #删除指定的键并返回相应的值，如果字典中没有该键则显示 KeyError 错误
 'c'
dict_
{0: 'a', 1: 'b', 3: 'd'}

dict_.popitem() #打印删除的键值对（以元组的形式返回），随机返回并删除字典中的一对键和值(一般删除末尾对)
(3, 'd')
dict_
Out[32]: {0: 'a', 1: 'b'}

dict_.clear() #清空字典
dict_
{ }

del dict_  #直接删除字典
dict_
Traceback (most recent call last):

  File "<ipython-input-37-247f529b331d>", line 1, in <module>
    dict_

NameError: name 'dict_' is not defined

• 修改字典中的元素

dictionary = dict(zip(list(range(5)),[str(x) for x in range(5)])) #创建字典
dictionary
{0: '0', 1: '1', 2: '2', 3: '3', 4: '4'}

print(2 in dictionary) # 检查健2是否在dictionary中
True

dictionary[2] = 'xiugai' # 修改健2对应的值'2'，变为'xiugai'
print(dictionary)
{0: '0', 1: '1', 2: 'xiugai', 3: '3', 4: '4'}

• fromkeys()的例子

print(dictionary)
{0: '0', 1: '1', 2: 'xiugai', 3: '3', 4: '4'}

x = dictionary.fromkeys([1,2,3],'xyz')   # fromkeys() 在原有的字典中声明一个新的字典
x
{1: 'xyz', 2: 'xyz', 3: 'xyz'}

y = {}.fromkeys(['a','b','c'], ['a','b','c'])
y
{'a': ['a', 'b', 'c'], 'b': ['a', 'b', 'c'], 'c': ['a', 'b', 'c']}

• 字典的循环迭代

x={'a': 1, 'b': 2, 'c': 3, 1: 'a'}

for i in x:
    print(i)
    
a
b
c
1

for i in x:
    print(i, x[i])
    
a 1
b 2
c 3
1 a

for i, j in x.items():
    print(i, j)
    
a 1
b 2
c 3
1 a