Python zero-based introduction to the ninth dictionary

1. Definition of dictionary
The characteristic of a dictionary is that the symbol of the dictionary is curly brackets, and the elements in the dictionary use key-value pairs. A key-value pair acts as a data item.
2. How to create a dictionary
(1) Use the definition method

dict1={'李宁':'一切皆有可能','耐克':'Just do it','阿迪达斯':'Impossible is nothing','鱼C工作室':'编程让世界更美好'}
print("鱼C工作室的口号是:",dict1["鱼C工作室"])print("\n")
dict2={1:'one',2:'two',3:'three'}#可以使用键作为索引获得相应的值。print(dict2[1])print('\n')

2. Use the dict() function to create a dictionary
It is worth noting What's more, dict() has only one parameter

#之所以会有那么多的括号，是因为dict函数只有一个参数
dict3=dict((('F',70),('i',105),('s',115),('h',104),('C',67)))
print(dict3)
print('\n')

(3) Use dict()+keyword parameters to create a dictionary
It is worth noting that: keyword parameters are not No quotation marks

dict4=dict(小甲鱼="编程让世界更加美好",苍井空="让AV征服宅男")print(dict4)

##3. Modify the items in the dictionary

(1) Modify the items that exist in the dictionary

dict4['苍井空']="AV不是宅男的福利"print(dict

(2) Modify items that do not exist in the dictionary

This is special, not only will no exception occur, but the data item will be inserted into the dictionary

dict4['爱迪生']="天才是99%的汗水加上1%的灵感"print(dict4)

4. Dictionary’s built-in function

(1)fromkeys(S[,v]) creates a dictionary and returns a dictionary. The default value of the second parameter is
None.

dict1={}dict1=dict1.fromkeys((1,2,3))
print(dict1)
print("\n")dict1=dict1.fromkeys((1,2,3),('numbers'))
print(dict1)

(2)keys() function: get all the keys of the dictionary

dict1=dict1.fromkeys(range(32),"赞")
print(dict1)for eachkey in dict1.keys():     
print(eachkey,end=" ")
print("\n")

(3)values() function: get all the keys of the dictionary Value

#values()所有值的集合for eachvalue in dict1.values():     print(eachvalue,end=" ")print("\n")

(4)items() function: Get all items of the function

for eachitem in dict1.items():     print(eachitem,end=" ")

(5)get () function gets the value corresponding to the dictionary key. If it does not exist, it returns None

str1=dict1.get(32)
print(str1)

(6) in or not in membership determiner: determine whether a key or value In the dictionary

print("\n")print(32 in dict1)print("\n")

(7)clear(): Clear all items in the dictionary

dict1.clear()print(dict1)

(8 )update() function: Use one dictionary to update the contents of another dictionary

a={1:"one"}
b={1:"two"}a.update(b)
print(a)

Finally, let’s talk about the difference between using “=” (assignment symbol) and using the copy function:

In general, using the assignment symbol only creates a label pointing to the data, but it still shares the same data, similar to a person's name. When using functions, the data has absolutely no relationship.

print("\n")
list1=['1','2','3']
list2=list1[:3]
list3=list1print(id(list1))
print(id(list2))
print(id(list3))
print(list2)
print(list3)
list1[0]="666"
print(list2)
print(list3)
#根据id可知，字典的赋值操作创建了一个指向
#数据的一个标签，并不是真正意义上的拷贝
a={"姓名":"小甲鱼"}
b=aprint(id(a))print(id(b))print(b)
#将a指向了空字典，而不是改变其数据的大小
#这里类似于指针的赋值，指针的赋值是将地址的赋值
#而不是数据的赋值a={}
#空集类似于空指针print(id(a))print(a)print(b)
#赋值与全拷贝函数,区别类似于上面a={1:'one',2:'two',3:'three'}
b=a.copy()
c=aprint(id(a))print(id(b))print(id(c))print(a)print(b)print(c)

The dictionary knowledge ends here. If there is more, I will add it in time.

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