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HomeBackend DevelopmentPython TutorialBasics | Detailed explanations of 11 Python dictionary usages

This issue brings you a comprehensive analysis of the 11 methods of Python dictionary, I hope it will be helpful to you You helped.

Dictionary (Dictionary) is a commonly used data structure provided by Python. It is used to store data with mapping relationships, consisting of key (key) and value (value) It is composed of in pairs, the key and value are separated by colon:, and the items are separated by commas. The entire dictionary is enclosed by curly brackets {}, and the format is as follows:
dic = {key1 : value1, key2 : value2 }

Dictionaries are also called associative arrays or hash tables. Here are several common ways to create dictionaries:

# 方法1
dic1 = { 'Author' : 'Python当打之年' , 'age' : 99 , 'sex' : '男' }

# 方法2
lst = [('Author', 'Python当打之年'), ('age', 99), ('sex', '男')]
dic2 = dict(lst)

# 方法3
dic3 = dict( Author = 'Python当打之年', age = 99, sex = '男')

# 方法4
list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', 99, '男']
dic4 = dict(zip(list1, list2))
字典创建的方式还有很多种,这里不再赘述。
字典由 dict 类代表,可以使用 dir(dict) 来查看该类包含哪些方法,输入命令,可以看到如下输出结果:
print('methods = ',methods)

methods = ['__class__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']
字典的方法和属性有很多种,这里我们重点介绍以下11种方法:
['clear', 'copy', 'fromkeys', 'get', 'items', 'keys', 'pop', 'popitem', 'setdefault', 'update', 'values']

1. dict.clear()

clear() 用于清空字典中所有元素(键-值对),对一个字典执行 clear() 方法之后,该字典就会变成一个空字典:
list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', 99, '男']
dic1 = dict(zip(list1, list2))
# dic1 = {'Author': 'Python当打之年', 'age': 99, 'sex': '男'}

dic1.clear()
# dic1 = {}


2. dict.copy()

copy() 用于返回一个字典的浅拷贝:
list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', 99, '男']
dic1 = dict(zip(list1, list2))

dic2 = dic1 # 浅拷贝: 引用对象
dic3 = dic1.copy() # 浅拷贝:深拷贝父对象(一级目录),子对象(二级目录)不拷贝,还是引用
dic1['age'] = 18

# dic1 = {'Author': 'Python当打之年', 'age': 18, 'sex': '男'}
# dic2 = {'Author': 'Python当打之年', 'age': 18, 'sex': '男'}
# dic3 = {'Author': 'Python当打之年', 'age': 99, 'sex': '男'}
其中 dic2 是 dic1 的引用,所以输出结果是一致的,dic3 父对象进行了深拷贝,不会随dic1 修改而修改,子对象是浅拷贝所以随 dic1 的修改而修改,注意父子关系。
拓展深拷贝:copy.deepcopy()
import copy

list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', [18,99], '男']
dic1 = dict(zip(list1, list2))

dic2 = dic1
dic3 = dic1.copy()
dic4 = copy.deepcopy(dic1)
dic1['age'].remove(18)
dic1['age'] = 20

# dic1 = {'Author': 'Python当打之年', 'age': 20, 'sex': '男'}
# dic2 = {'Author': 'Python当打之年', 'age': 20, 'sex': '男'}
# dic3 = {'Author': 'Python当打之年', 'age': [99], 'sex': '男'}
# dic4 = {'Author': 'Python当打之年', 'age': [18, 99], 'sex': '男'}
dic2 是 dic1 的引用,所以输出结果是一致的;dic3 父对象进行了深拷贝,不会随dic1 修改而修改,子对象是浅拷贝所以随 dic1 的修改而修改;dic4 进行了深拷贝,递归拷贝所有数据,相当于完全在另外内存中新建原字典,所以修改dic1不会影响dic4的数据

3. dict.fromkeys()

fromkeys() 使用给定的多个键创建一个新字典,值默认都是 None,也可以传入一个参数作为默认的值:
list1 = ['Author', 'age', 'sex']
dic1 = dict.fromkeys(list1)
dic2 = dict.fromkeys(list1, 'Python当打之年')

# dic1 = {'Author': None, 'age': None, 'sex': None}
# dic2 = {'Author': 'Python当打之年', 'age': 'Python当打之年', 'sex': 'Python当打之年'}

4. dict.get()

get() 用于返回指定键的值,也就是根据键来获取值,在键不存在的情况下,返回 None,也可以指定返回值:
list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', [18,99], '男']
dic1 = dict(zip(list1, list2))

Author = dic1.get('Author')
# Author = Python当打之年
phone = dic1.get('phone')
# phone = None
phone = dic1.get('phone','12345678')
# phone = 12345678


5. dict.items()

items() 获取字典中的所有键-值对,一般情况下可以将结果转化为列表再进行后续处理:
list1 = ['Author', 'age', 'sex']
list2 = ['Python当打之年', [18,99], '男']
dic1 = dict(zip(list1, list2))
items = dic1.items()
print('items = ', items)
print(type(items))
print('items = ', list(items))

# items = dict_items([('Author', 'Python当打之年'), ('age', [18, 99]), ('sex', '男')])
# <class &#39;dict_items&#39;>
# items = [(&#39;Author&#39;, &#39;Python当打之年&#39;), (&#39;age&#39;, [18, 99]), (&#39;sex&#39;, &#39;男&#39;)]


6. dict.keys()

keys() 返回一个字典所有的键:
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
keys = dic1.keys()
print(&#39;keys = &#39;, keys)
print(type(keys))
print(&#39;keys = &#39;, list(keys))

# keys = dict_keys([&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;])
# <class &#39;dict_keys&#39;>
# keys = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]


7. dict.pop()

pop() 返回指定键对应的值,并在原字典中删除这个键-值对:
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
sex = dic1.pop(&#39;sex&#39;)
print(&#39;sex = &#39;, sex)
print(&#39;dic1 = &#39;,dic1)

# sex = 男
# dic1 = {&#39;Author&#39;: &#39;Python当打之年&#39;, &#39;age&#39;: [18, 99]}


8. dict.popitem()

popitem() 删除字典中的最后一对键和值:
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
dic1.popitem()
print(&#39;dic1 = &#39;,dic1)

# dic1 = {&#39;Author&#39;: &#39;Python当打之年&#39;, &#39;age&#39;: [18, 99]}


9. dict.setdefault()

setdefault() 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:
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
dic1.setdefault(&#39;Author&#39;, &#39;当打之年&#39;)
print(&#39;dic1 = &#39;,dic1)
# dic1 = {&#39;Author&#39;: &#39;Python当打之年&#39;, &#39;age&#39;: [18, 99], &#39;sex&#39;: &#39;男&#39;}
dic1.setdefault(&#39;name&#39;, &#39;当打之年&#39;)
print(&#39;dic1 = &#39;,dic1)
# dic1 = {&#39;Author&#39;: &#39;Python当打之年&#39;, &#39;age&#39;: [18, 99], &#39;sex&#39;: &#39;男&#39;, &#39;name&#39;: &#39;当打之年&#39;}


10. dict.update(dict1)

update() 字典更新,将字典dict1的键-值对更新到dict里,如果被更新的字典中己包含对应的键-值对,那么原键-值对会被覆盖,如果被更新的字典中不包含对应的键-值对,则添加该键-值对
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
print(&#39;dic1 = &#39;,dic1)
# dic1 = {&#39;Author&#39;: &#39;Python当打之年&#39;, &#39;age&#39;: [18, 99], &#39;sex&#39;: &#39;男&#39;}

list3 = [&#39;Author&#39;, &#39;phone&#39; ]
list4 = [&#39;当打之年&#39;, 12345678]
dic2 = dict(zip(list3, list4))
print(&#39;dic2 = &#39;,dic2)
# dic2 = {&#39;Author&#39;: &#39;当打之年&#39;, &#39;phone&#39;: 12345678}

dic1.update(dic2)
print(&#39;dic1 = &#39;,dic1)
# dic1 = {&#39;Author&#39;: &#39;当打之年&#39;, &#39;age&#39;: [18, 99], &#39;sex&#39;: &#39;男&#39;, &#39;phone&#39;: 12345678}

11. dict.values()

values() 返回一个字典所有的值:
list1 = [&#39;Author&#39;, &#39;age&#39;, &#39;sex&#39;]
list2 = [&#39;Python当打之年&#39;, [18,99], &#39;男&#39;]
dic1 = dict(zip(list1, list2))
values = dic1.values()
print(&#39;values = &#39;, values)
print(type(values))
print(&#39;values = &#39;, list(values))

# values = dict_values([&#39;Python当打之年&#39;, [18, 99], &#39;男&#39;])
# <class &#39;dict_values&#39;>
# values = [&#39;Python当打之年&#39;, [18, 99], &#39;男&#39;]

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