Lists and dictionaries
mutable data types in Python are: List and dictionary immutable types: numbers, strings, tuples speak lists and dictionaries today
A. List
1. Concept:
Variables: Use variables to store data, but variable store data can only store one data at a time
Question: What do I do if I want to store multiple data at once?
#需求: Store 5 People's age, ask for an average of age
Age1 = 10
Age2 = 15
Age3 = 30
Age4 = 17
Age5 = 24
Avg = (age1 + age2 + age3 + age4 + age5)/5
Workaround: Take the list
Function: Equivalent to a container that can store multiple data at the same time
Essence: A list is an ordered set of
Description: Ordered refers to the order in which the stored order of storage is the same as the order in which it is stored in memory.
2. Create a list: num = 10
Syntax: variable name = List
? List name = [Data 1, Data 2 ..... ]
Description
? A. Defining a list by []
? B. The data stored in the list is called an element
? C. The elements in the list are numbered from beginning to end, numbering starting from 0, which is called index, corner or subscript
? D. Index range: Number of elements in the 0~ list-1 "0~ The length of the list-1"
? E. Exceeding the index range: The index of the list is out of bounds
3. Access to elements in the list 3.1 Value
Code Demo:
#元素的访问
#1. Take a value
#语法: List name [index]
#索引: 0~4
List1 = [543,5,46,56,6]
NUM1 = list1[2]
Print (list1[2])
Print (NUM1)
#列表索引越界
#print (list1[-10]) #IndexError: List index out of range
#print (List1[5])
3.2. Replacement value
#语法: The element in the list name [index] = new Value list is essentially a variable, so the action to replace it is actually to reassign the variable "
LIST1[2] = 100
Print (list1[2])
4. Actions in the list
Code Demo:
#列表的操作
#1. List combination: +
List1 = [54,5,45,4]
List2 = ["abc", "Fhj", "GHFJG"]
#列表的组合并没有修改原来的列表, instead, a new list is generated
List3 = List1 + list2
Print (LIST3)
Print (List1)
Print (LIST2)
#2. Duplicate list elements: *
#2.1 You can store duplicate elements in a list
L1 = [20,20,40,45,54,20]
Print (L1)
#2.2
L2 = [10,20,30]
L3 = L2 * 3
Print (L3)
? #3. Determine whether an element is in the list: member operator [INT not in]
#注意: The result of a member operator operation is a Boolean value
#一般结合if语句使用
L4 = [34,54,56, "ANC"]
Print (in L4)
Print (in L4)
Print (in L4)
Print (L4)
"""
True
False
False
True
#4. Intercepting "slices" of the list
#4.1 intercept The specified interval: list name [start index: End index]
#特点: Related to the interval, Baotou does not pack tail front closed after the opening interval: [2,4)
L5 = [34,54,56, "ANC", 5,65,76,7677]
Print (L5[2:4])
#4.2 intercept from the beginning to the specified position
Print (L5[0:5])
Print (L5[:5])
#4.3 intercept from the specified position to the end
Print (L5[3:7])
Print (l5[3:])
#注意; If you want to take the last element, you can go beyond the scope of the index, in which case there will be no error
Print (l5[3:20])
5. Features of the list
Syntax: List name. function name ()
#1. Adding elements
#1.1 append (): Appending elements at the end of a list element
LIST11 = [10,20,30]
Print (LIST11)
#追加单个元素
List11.append (40)
Print (LIST11)
#追加多个元素
#list11. Append (50,60) #错误演示
#注意: Append multiple elements using the APPEND function, cannot be appended directly, append by the form of a list
List11.append ([50,60])
Print (LIST11)
#1.2 Extend (): extending, adding elements at the end of the list
list12 = [10,20,30]
Print (list12)
#追加单个元素
#list12. Extend (#错误演示): Extend cannot add a single element directly
# #iterable: The iterator of an iteration
#追加多个元素
#注意: Adding multiple elements using extend is still added as a list, but actually adding just the element "break add"
List12.extend ([50,60])
Print (list12)
Print ("~~~~~~~~")
#1.3 Insert (), insert, insert element at specified index
#格式: Insert (index, inserted data)
list13 = [10,20,30]
Print (LIST13)
List13.insert (2,40)
Print (LIST13)
#注意: Inserts one by one lists, inserts the entire list into the original list
List13.insert (1,[50,60])
Print (LIST13)
#2. Deleting elements
#2.1 Pop (index); Eject to remove the element at the specified index in the list
list21 = [10,20,30,40,50,60]
Print (list21)
#pop默认移除的是最后一个元素, the resulting result is the removed element
RESULT1 = List21.pop ()
Print (list21)
Print (RESULT1)
#移除指定位置的元素
List21.pop (2)
Print (list21)
#2.2 Remove (Element): Remove, Feature: Removes the element in the list "the first element in the list that can match from 0"
list22 = [10,20,30,40,50,60]
Print (list22)
List22.remove #等价于list22. Pop (0)
Print (list22)
#需求: Remove all the numbers in the list 10
list23 = [10,20,30,40,50,60,10,10,10,10,10,10]
"" "List23.remove (10)
Print (list23)
List23.remove (10)
Print (list23)
List23.remove (10)
Print (list23)
"""
num = 0
element = 10
Cou = List23.count (Element)
While Num < cou:
List23.remove (Element)
Print (list23)
num + = 1
Print (list23)
? #2.3 Clear (): Clear, clear all the elements in the list, the original list becomes empty list
List24 = [10,20,30,40,50,60,10,10,10,10,10,10]
List24.clear ()
Print (LIST24)
? #3. Get
#语法: Feature name (list name)
#3.1 len () length, gets the width of the list "gets the number of elements in the list"
LIST31 = [10,20,30,40,50,60,10,10,10,10,10,10]
length = Len (list31)
?
#3.2 Max (); Gets the maximum value of the element in the list min () min
Print (max (LIST31))
Print (min (list31))
?
#3.3 index (): index, the index value corresponding to the first element that is matched to from a list
INX1 = List31.index (10)
Print (INX1)
?
#3.4 count (), number to find the number of occurrences of the specified element in the list
c = List31.count (10)
Print (c)
?
#4. Other
#4.1 reverse () invert to reverse the output of the elements in the list
LIST41 = [10,20,30,40,50,60,10,10,10,10,10,10]
List41.reverse ()
Print (LIST41)
?
#4.2 sort () sorted by default ascending sort, note: internal operation in list
#升序
List41.sort ()
Print (LIST41)
#降序
List41.sort (Reverse=true)
Print (LIST41)
?
Sort #sorted () by default in ascending order, note: Generate a new list
List42 = [10,20,30,40,50,60,10,10,10,10,10,10]
#升序
NewList1 = sorted (list42)
Print (LIST42)
Print (NEWLIST1)
#降序
NewList2 = sorted (list42,reverse=true)
Print (NEWLIST2)
?
#按照长度排序
List43 = ["FHJDHF", "G", "GFG"]
NewList3 = sorted (List43,key=len)
Print (NEWLIST3)
?
#4.3 Copy "Face question"
#浅拷贝
#深拷贝
#a. From the memory point of view
#浅拷贝: Referencing "stack space"
List44 = [23,45,98]
List45 = List44
LIST45[1] = 100
Print (LIST44)
Print (LIST45)
Print (ID (list44) = = ID (list45))
?
?
#深拷贝: Memory "entity, heap space"
List51 = [23,45,98]
List52= list51.copy ()
LIST52[1] = 100
Print (LIST51)
Print (LIST52)
Print (ID (list51) = = ID (list52))
Two. Dictionaries
1. Concept:
Thinking problem: Saving scores for multiple students
Solution: Dictionary, the student as key, the results as value, to store, easy to find "one by one correspondence"
Nature: Also a container for storing data
Features: Data stored as key-value pairs, with the advantage of Quick Find
Note: Dictionaries are unordered
Features of key
：? A. The key in the dictionary must be unique
? B. The key in the dictionary must be immutable
? List is mutable and cannot function as key
? A tuple is immutable and can act as a key, a numeric type, and a string can act as key
2. Create:
syntax: dictionary name = {key1:value1,key2:value2 ...}
Code Demo:
#1. Creating a Dictionary
#创建一个空字典
Dict1 = {}
#创建有键值对的字典
Dict2 = {"Zhangsan": $, "Jack": 90}
Print (DICT2)
3. Method:
1 Get key: Syntax dictionary name. Key
2 Gets the value: syntax dictionary name. Value
3 Modify or add: Syntax: dictionary name [Key]=value, if there is a key to modify, otherwise add a new key value pair
4 Delete: Syntax: dictionary name. Pop (key) deletes the specified Popitem () when the last one in the dictionary is deleted
Python Learning path 04--list and dictionary
