table of Contents
1.5 Check whether an element is a member of a sequence
1.6 Calculate the length, maximum and minimum of the sequence
1.7 Other built-in functions of sequence
2.1 Creation and deletion of lists
2.4 Add, modify, delete list elements
2.5 Statistics and calculations on the list
3.1 Creation and deletion of tuples
4.1 Dictionary creation and deletion
4.2 Accessing the dictionary through key-value pairs
4.3 Iterating over the dictionary
4.4 Add, modify and delete dictionary elements
5.2 Adding and deleting collections
One: Sequence
In python, sequence is the most basic data structure, it is a continuous memory space used to store multiple values.
There are 5 commonly used sequence structures built into python, namely lists, tuples, sets, dictionaries and strings.
Next, we will introduce the common operations of the sequence.
1.1 Index
Every element in python has a number, which also becomes an index. This index is incremented from 0.
[Note]: Python's index is special, its index can be negative, and the index of negative number is counted from right to left.
That is to count from the last element, that is, the index value of the last element is -1.
verse = ["春天","夏天","秋天","冬天"]
print(verse[2]) #秋天
print(verse[-1]) #冬天1.2 Slicing
Slicing is another way to access elements in a sequence, it can access elements within a certain range. A new sequence can be generated through the slicing operation.
The slicing operation syntax:
sname[start : end : step] #Use a colon, not a comma, the interval is left closed and right open
verse = ["春天","夏天","秋天","冬天"]
print(verse[1:3:1]) #['夏天', '秋天']1.3 Sequence addition
In python, two types of sequence addition operations are supported, that is, to connect two sequences without removing duplicate elements, using the (+) operator to achieve
verse = ["春天","夏天","秋天","冬天"]
verse2 = ["昨天","今天","明天"]
print(verse+verse2)
#['春天', '夏天', '秋天', '冬天', '昨天', '今天', '明天'][Explanation]: When adding sequences, the same type of sequence means that the same is a list, tuple, set, etc., and the types of elements in the sequence can be different .
1.4 Sequence multiplication
In python, multiplying a sequence by the number n will generate a new sequence. The content of the new sequence is the result of the original sequence being repeated n times.
phone = ["apple","华为","小米"]
print(phone*3)
#['apple', '华为', '小米', 'apple', '华为', '小米', 'apple', '华为', '小米']1.5 Check whether an element is a member of a sequence
The in keyword checks whether an element is a member of the sequence
The not in keyword implements to check whether an element is not included in the specified sequence
1.6 Calculate the length, maximum and minimum of the sequence
len() function: returns how many elements the sequence contains
max() function: returns the largest element in the sequence
min() function: returns the smallest element in the sequence
num = [12,14,66,9,245,1,90]
print(len(num)) #7
print(max(num)) #245
print(min(num)) #11.7 Other built-in functions of sequence
list(): convert a sequence to a list
str(): Convert sequence to string
sum(): Calculate the sum of elements
sorted(): sort the elements
reversed(): Reverse the elements in the sequence
enumerate(): Combine the sequence into an index sequence, which is mostly used in a for loop
Second list
2.1 Creation and deletion of lists
1) Use the assignment operator to create the list directly
list1 = ["我是最棒的","我是做大事的人","我一定会成功"]2) Create an empty list
emptylist = []3) Create a list of values
Use the list() function
list2 = list(["hello","world"])
#注意中括号不能省掉You can also use the list() function to directly convert the looped result of the range() function into a list
list(range(10,20,2))4) Delete the list
del listname2.2 Access list
list1 = ["我是最棒的","我是做大事的人","我一定会成功"]
print(list1[2]) #我一定会成功You can also use the index() mentioned earlier
2.3 Traverse the list
1) Directly use for loop to achieve
for item in listname:
print(item)2) Use for loop and enumerate() function to output index value and element content at the same time
list1 = ["我是最棒的","我是做大事的人","我一定会成功"]
for index, item in enumerate(list1):
print(index,item) #我一定会成功
#0 我是最棒的
#1 我是做大事的人
#2 我一定会成功Supplement: The print() function in python wraps output by default. In order not to wrap the output, we can use "end = '' "in print()
2.4 Add, modify, delete list elements
1) Add elements
In addition to using the plus sign "+" to connect the two sequences, we recommend using the append() method .
phone = ["oppo","三星","小米","华为"]
phone.append("apple")
print(len(phone))
print(phone)In addition, you can also use the insert() method to insert elements into the specified position of the list, but this method is not efficient.
Supplement: If you want to add all the elements in one list to another list, you can use the extend() method of the list object.
phone1 = ["oppo","三星","小米","华为"]
phone2 = ["诺基亚","魅族"]
phone1.extend(phone2)
print(phone1)
#['oppo', '三星', '小米', '华为', '诺基亚', '魅族']2) Modify elements
To modify an element, you only need to get the element through the index, and then re-assign it.
phone1 = ["oppo","三星","小米","华为"]
phone1[2]= "红米"
print(phone1)
# ['oppo', '三星', '红米', '华为']3) Delete elements
- Delete according to index
del phone[1]- Delete based on element value
phone.remove("华为")2.5 Statistics and calculations on the list
1) Get the number of occurrences of the specified element
phone1 = ["oppo","三星","小米","华为","oppo"]
print(phone1.count("oppo")) #22) Get the index of the first occurrence of the specified element
phone1 = ["oppo","三星","小米","华为","oppo"]
print(phone1.index("oppo")) #3) The sum of the elements of the list of statistical values
grade = [222,44,66,88,9,2]
print(sum(grade)) #4312.6 Sort the list
1) Use the sort() method: The original list will change
grade = [222,44,66,88,9,2]
print(grade.sort()) #None
print(grade) #[2, 9, 44, 66, 88, 222]The default is ascending order, if you want to sort in descending order, you need to use reverse = True
grade = [222,44,66,88,9,2]
grade.sort(reverse=True)
print(grade) #[222, 88, 66, 44, 9, 2]2) Use the built-in sorted() function to achieve
Note that after the sorted() method is sorted, the order of the elements of the original list remains unchanged, because a copy of the original list will be created.
grade = [222,44,66,88,9,2]
new_grade= sorted(grade)
print(grade) #[222, 44, 66, 88, 9, 2]
print(new_grade) #[2, 9, 44, 66, 88, 222]2.7 List comprehensions
Use list comprehensions to quickly generate a list
list = [expression for var in range]import random
randomnumber = [random.randint(10,100) for i in range(10)]
print(randomnumber)
#[84, 20, 73, 31, 31, 76, 30, 80, 45, 53]2.8 Two-dimensional list
1) Directly define a two-dimensional list
list1 = [['a','b','c'],['d','e','f'],['q','w','e'],['a','s','d']]
print(list1)
# [['a', 'b', 'c'], ['d', 'e', 'f'], ['q', 'w', 'e'], ['a', 's', 'd']]2) Use nested for loop creation
arr = []
for i in range(4):
arr.append([])
for j in range(5):
arr[i].append(j)
print(arr)
# [[0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4]]3) Use list comprehension to create
arr = [[j for j in range(5)] for i in range(4)]
print(arr)
# [[0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4], [0, 1, 2, 3, 4]]Triad
3.1 Creation and deletion of tuples
1) Use the assignment operator to directly create a tuple
num1 = (12,34,67,11,3,99)
print(num1)
print(type(num1))
#(12, 34, 67, 11, 3, 99)
#<class 'tuple'>2) Create empty tuple
emptytuple = ()3) Create numeric elements
print(tuple(range(10,20,2)))
#(10, 12, 14, 16, 18)4) Delete elements
del tuplename3.2 Accessing tuple elements
team = ("火箭","骑士","快船","湖人")
print(team[1])
for index, item in enumerate(team):
print(index,item)
#骑士
#0 火箭
#1 骑士
#2 快船
#3 湖人
3.3 Modify tuple elements
A tuple is an immutable sequence, so we cannot modify its single element value,
But the tuple is not completely unmodifiable, we can reassign the tuple
coffeename = ("拿铁","卡布奇诺","曼特宁")
coffeename = ("拿铁2","卡布奇诺3")
print(coffeename) #('拿铁2', '卡布奇诺3')3.4 Tuple comprehension
#To convert to a tuple, use the tuple() function
import random
randomnumber = (random.randint(10,100) for i in range(10))
randomnumber = tuple(randomnumber)
print(randomnumber)
# (69, 30, 31, 50, 22, 86, 50, 32, 29, 85)Four. Dictionary
Similar to a list, a dictionary is also a variable sequence, but unlike a list, it is an unordered variable sequence.
The saved content is stored in the form of key-value pairs.
The key is unique and there are multiple values
The same key is not allowed to appear twice, if it appears twice, the latter value will be remembered .
4.1 Dictionary creation and deletion
1) To create a dictionary, a colon is used to separate the key and value, and two adjacent elements are separated by a comma, and all elements are placed in a pair of "{ }".
dictionary = {"qq":"282439859","bolg":"yezonghui"}
print(dictionary)
print(type(dictionary))
#{'qq': '282439859', 'bolg': 'yezonghui'}
#<class 'dict'>2) Create a dictionary through the mapping function
di = dict(zip(list1,list2))Supplement: zip() function: used to combine elements at corresponding positions of multiple lists or tuples into tuples, and return a zip object containing these contents
name = ["q","w","e","r"]
sign = ["1","2","3","5"]
dirctionary2 = dict(zip(name,sign))
print(dirctionary2)
# {'q': '1', 'w': '2', 'e': '3', 'r': '5'}4.2 Accessing the dictionary through key-value pairs
Use [] or get() method
d1 = {"春天":"学语文","夏天":"学数学","秋天":"学英语","冬天":"学历史"}
print(d1["夏天"]) #学数学
print(d1.get("秋天")) #学英语4.3 Iterating over the dictionary
Get the dictionary view:
keys(): Get all keys in the dictionary
values(): Get all values in the dictionary
items(): Get all key and value pairs in the dictionary
d1 = {"春天":"学语文","夏天":"学数学","秋天":"学英语","冬天":"学历史"}
for item in d1.items():
print(item)
#('春天', '学语文')
#('夏天', '学数学')
#('秋天', '学英语')
#('冬天', '学历史')d1 = {"春天":"学语文","夏天":"学数学","秋天":"学英语","冬天":"学历史"}
for key,value in d1.items():
print(key,value)
#春天 学语文
#夏天 学数学
#秋天 学英语
#冬天 学历史4.4 Add, modify and delete dictionary elements
Add directly
d1 = {"春天":"学语文","夏天":"学数学","秋天":"学英语","冬天":"学历史"}
d1["今天"] = "学习"
print(d1)
#{'春天': '学语文', '夏天': '学数学', '秋天': '学英语', '冬天': '学历史', '今天': '学习delete
del d1["春天"]4.5 Dictionary comprehension
import random
ranomdict = {i:random.randint(10,100) for i in range(1,5)}
print(ranomdict)
#{1: 77, 2: 77, 3: 100, 4: 79}Five. Collection
5.1 Collection creation
1) Create directly using {}
set1 = {1,4,6,7}2) Created using the set() function
set1 = set(1,2,3,4,8)[Note]: When creating an empty dictionary, you can only use set(), because a pair of {} means creating an empty dictionary
5.2 Adding and deleting collections
1) Add elements to the collection using the add() method
2) Remove elements from the collection using remove()
5.3 Set operations
1) Are the two sets equal == or! =
2) Is it a subset issubset()
3) Whether it is a superset: issuperset()
4) Intersection: & or intersection()
5) Union: | or union()
6) Difference:-or difference()
[Note]: The learning of strings in the sequence will be summarized in the next blog