Python List in the standard library (list) Be similar to C/C++ In the array .
Python In the extension library ndarray Objects have many operations and lists (list) Similar to , Such as slicing 、 Element access , But they are two things , Don't get confused . About ndarray Basic operation of objects , Please refer to the blog https://blog.csdn.net/wenhao_ir/article/details/124416798
The importance of arrays to programming is self-evident , So this blog post summarizes Python List in the standard library (list) The operation of .
Sequence is Python The most basic data structure in .
Each value in the sequence has a corresponding position value , Call it an index , The first index is 0, The second index is 1, And so on .
The operations that can be performed by a sequence include indexing , section , Add , ride , Check members .
Besides ,Python There's a built-in way to determine the length of the sequence and determine the maximum and minimum elements .
Python Yes 6 Built in types of sequences , But the most common are lists and tuples .
Lists are the most commonly used Python data type , The data items of a list do not need to have the same type .
Create a list , Just enclose the different data items separated by commas in square brackets .
list1 = ['Google', 'CSDN', 1997, 1999]
list2 = [1, 2, 3, 4, 5]
list3 = ['red', 'green', 'blue', 'yellow', 'white', 'black']
The results are shown in the following figure ：
From the above results we can see that , stay Python Chinese is a word list Represents the of the list .
A list is essentially an object , So you can use the constructor to create , The code is as follows ：
list1 = list()
list1.append('Google')
list1.append('CSDN')
list1.append('1997')
list1.append('1999')
The operation results are as follows ：
From above , Obviously the first 1 Methods 2 This method is convenient . But when you want to use member functions append() When adding elements , If you use the first method ,Pycharm This is not recommended , As shown in the figure below ：
This list creation could be rewritten as a list literal.
This sentence means that the list should be created according to its original meaning . What is original meaning creation ？ A list is essentially an object , Since the object , Then use the constructor to initialize and create .
The following two articles explain the reasons for this problem ：
https://www.cnblogs.com/jiangxiaobo/p/11622730.html
https://zhuanlan.zhihu.com/p/222401764
The sample code is as follows ：
list1 = ['Google', 'CSDN', 1997, 1999]
print(list1[0])
print(list1[1])
print(list1[2])
The operation results are as follows ：
Except from left to right , Or from right to left , The sample code is as follows ：
list1 = ['Google', 'CSDN', 1997, 1999]
print(list1[-1])
print(list1[-2])
print(list1[-3])
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
list2 = list1[0:4]
Be careful ： The section is left closed and right open , namely [0:4] amount to [0,4)
The operation results are as follows ：
You can also combine positive and negative indexes ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
list2 = list1[0:-2]
above list1[0:-2] To intercept 0 To the last 2 Clips of , The operation results are as follows ：
Be careful ： In this case, we use the constructor to create the list , Instead of using brackets to create lists , otherwise Pycharm This is not recommended , As shown in the figure below ：
This list creation could be rewritten as a list literal.
This sentence means that the list should be created according to its original meaning . What is original meaning creation ？ A list is essentially an object , Since the object , Then use the constructor to initialize and create .
The following two articles explain the reasons for this problem ：
https://www.cnblogs.com/jiangxiaobo/p/11622730.html
https://zhuanlan.zhihu.com/p/222401764
The sample code is as follows ：
list1 = list()
list1.append('Google')
list1.append('CSDN')
list1.append('1997')
list1.append('1999')
The operation results are as follows ：
Pay special attention to ： When using method append() When the added element itself is also a list , This is the shallow copy operation , That is, the copied list value changes , Then the value of the corresponding element in the list will also change , The sample code is as follows ：
list1 = list()
list1.append('Google')
list1.append('CSDN')
list1.append('1997')
list1.append('1999')
list2 = [2010]
list1.append(list2)
list2[0] = 4444
The operation results are as follows ：
If it's a deep copy , that list1 No 4 Element values should be [2010] That's right .
If you want to make a deep copy of the list , You can do this as follows ：
import copy
list1 = list()
list1.append('Google')
list1.append('CSDN')
list1.append('1997')
list1.append('1999')
list2 = [2010]
list1.append(copy.deepcopy(list2))
list2[0] = 4444
The operation results are as follows ：
Of course, you can also use the method copy() Realization , Namely code ：
list1.append(copy.deepcopy(list2))
Can be replaced by
list1.append(list2.copy())
For general variables , The effect is a deep copy , The code is as follows ：
list1 = list()
list1.append('Google')
list1.append('CSDN')
list1.append('1997')
list1.append('1999')
value1 = 2030
list1.append(value1)
value1 = 4444
The operation results are as follows ：
As we can see from the above example , Method append() Is to make the appended list as a whole ( As an element ) Added to the original list , Sometimes we want to append multiple values from another sequence at the end of the list at once , This time you can use the method extend() Realization .
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'Taobao']
list2 = [1997, 1999, 1998]
list1.extend(list2)
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'Taobao', 1997, 1999, 1998, 1999]
list1.insert(3, 'Tecent')
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
del list1[2]
The operation results are as follows ：
From the above results , The first 2 Elements ’tencent’ Been deleted .
Method pop() The grammar is as follows ：
list.pop([index=-1])
index – Optional parameters , To remove the index value of a list element , Cannot exceed the total length of the list , The default is index=-1, Delete the last list value .
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
list2 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
value1 = list1.pop()
value2 = list1.pop(1)
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998, 'CSDN']
list1.remove('CSDN')
The operation results are as follows ：
From the above results, we can see , Method remove() What is removed is the first matching element . The above string element ’CSDN’ There are two , But only the first one was deleted .
The sample code is as follows ：
len1 = len([1, 2, 3])
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
len2 = len(list1)
The operation results are as follows ：
The sample code is as follows ：
list1 = [456, 700, 200]
max1 = max(list1)
The operation results are as follows ：
The sample code is as follows ：
list1 = [456, 700, 200]
min1 = min(list1)
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
list2 = [4, 5, 6]
list3 = list1+list2
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
list2 = [4, 5, 6]
list3 = list1*2
list4 = list2*3
The operation results are as follows ：
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'tencent', 1997, 1999, 1998]
bool1 = 'CSDN' in list1
bool2 = 'zhihu' in list1
The operation results are as follows ：
List nesting , Essentially, a list can also be used as an element of a list .
The sample code is as follows ：
list1 = [['Google', 'CSDN', 'tencent'], [1997, 1999, 1998]]
a1 = list1[0][1]
b1 = list1[1][2]
The operation results are as follows ：
Be careful , For sentences ：
a1 = list1[0][1]
b1 = list1[1][2]
Can not be like ndarray The object is written as follows ：
a1 = list1[0, 1]
b1 = list1[1, 2]
Error will be reported at this time ：
ndarray See the following blog post for details of accessing multidimensional matrix elements of ：
https://blog.csdn.net/wenhao_ir/article/details/124419922
The sample code is as follows ：
import operator
a = [1, 2]
b = [2, 3]
c = [2, 3]
bool1 = operator.eq(a, b)
bool2 = operator.eq(c, b)
The operation results are as follows ：
The sample code is as follows ：
list1 = [123, 'Google', 'CSDN', 'Taobao', 123]
count1 = list1.count(123)
count2 = list1.count('CSDN')
The operation results are as follows ：
Method index() The grammar is as follows ：
list.index(x[, start[, end]])
x-- Objects found .
start-- Optional , The starting point of the search .
end-- Optional , End of search .
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'Taobao', 1997, 1999, 1998, 1999]
index1 = list1.index('CSDN')
index2 = list1.index(1999)
The operation results are as follows ：
In the list 1999 There are two , It can be seen that the first index is returned .
The sample code is as follows ：
list1 = [1, 2, 3, 4, 5, 6, 7]
list1.reverse()
The operation results are as follows ：
Method sort() The grammar is as follows ：
list.sort( key=None, reverse=False)
key – The value used for comparison , Optional parameters .
reverse – Sort rule ,reverse = True Descending , reverse = False Ascending （ Default ）.
The sample code is as follows ：
list1 = [1, 5, 3, 9, 7, 4, 2, 8, 6]
list1.sort()
list2 = [1, 5, 3, 9, 7, 4, 2, 8, 6]
list2.sort(reverse=True)
The operation results are as follows ：
About the way sort() The first parameter of key Usage of , It's a long story , For details, please refer to another blog post ：
https://blog.csdn.net/wenhao_ir/article/details/125406092
The sample code is as follows ：
list1 = ['Google', 'CSDN', 'Taobao', 1997, 1999, 1998, 1999]
list1.clear()
The operation results are as follows ：
Method copy() An example of the use of ：
list1 = ['Google', 'CSDN', 'Taobao', 1997, 1999, 1998, 1999]
list2 = list1.copy()
list1[0] = 'Facebook'
The operation results are as follows ：
From the above code and running results, we can see , Method copy() It's a deep copy .
Method copy.append() An example of the use of ：
import copy
list1 = ['Google', 'CSDN', 'Taobao', 1997, 1999, 1998, 1999]
list2 = copy.deepcopy(list1)
list1[0] = 'Facebook'
The operation results are as follows ：
From the above code and running results, we can see , Method copy.append() It is also a deep copy .
The sample code is as follows ：
list1 = ['Google', 'Taobao', 'CSDN', 'Baidu']
tuple1 = tuple(list1)
The operation results are as follows ：
Detailed operations on tuples , You can refer to my other blog post , Links are as follows ：
https://blog.csdn.net/wenhao_ir/article/details/125407815
Reference material ：
https://blog.csdn.net/wenhao_ir/article/details/125100220
