标签：11 index obj Python list Lists lists print
The most basic data structure in Python is the sequence. Each element of a sequence is assigned a number - its position or index. The first index is zero, the second index is one, and so forth.
Python has six built-in types of sequences, but the most common ones are lists and tuples, which we would see in this tutorial.
There are certain things you can do with all the sequence types. These operations include indexing, slicing, adding, multiplying, and checking for membership. In addition, Python has built-in functions for finding the length of a sequence and for finding its largest and smallest elements.
Python Lists
The list is the most versatile datatype available in Python, which can be written as a list of comma-separated values (items) between square brackets. Important thing about a list is that the items in a list need not be of the same type.
Creating a list is as simple as putting different comma-separated values between square brackets. For example −
list1 = ['physics', 'chemistry', 1997, 2000]; list2 = [1, 2, 3, 4, 5 ]; list3 = ["a", "b", "c", "d"];
Similar to string indices, list indices start at 0, and lists can be sliced, concatenated and so on.
Accessing Values in Lists
To access values in lists, use the square brackets for slicing along with the index or indices to obtain value available at that index. For example −
Live Demo#!/usr/bin/python3
list1 = ['physics', 'chemistry', 1997, 2000]
list2 = [1, 2, 3, 4, 5, 6, 7 ]
print ("list1[0]: ", list1[0])
print ("list2[1:5]: ", list2[1:5])
When the above code is executed, it produces the following result −
list1[0]: physics list2[1:5]: [2, 3, 4, 5]
Updating Lists
You can update single or multiple elements of lists by giving the slice on the left-hand side of the assignment operator, and you can add to elements in a list with the append() method. For example −
Live Demo#!/usr/bin/python3
list = ['physics', 'chemistry', 1997, 2000]
print ("Value available at index 2 : ", list[2])
list[2] = 2001
print ("New value available at index 2 : ", list[2])
Note − The append() method is discussed in the subsequent section.
When the above code is executed, it produces the following result −
Value available at index 2 : 1997 New value available at index 2 : 2001
Delete List Elements
To remove a list element, you can use either the del statement if you know exactly which element(s) you are deleting. You can use the remove() method if you do not know exactly which items to delete. For example −
Live Demo#!/usr/bin/python3
list = ['physics', 'chemistry', 1997, 2000]
print (list)
del list[2]
print ("After deleting value at index 2 : ", list)
When the above code is executed, it produces the following result −
['physics', 'chemistry', 1997, 2000] After deleting value at index 2 : ['physics', 'chemistry', 2000]
Note − remove() method is discussed in subsequent section.
Basic List Operations
Lists respond to the + and * operators much like strings; they mean concatenation and repetition here too, except that the result is a new list, not a string.
In fact, lists respond to all of the general sequence operations we used on strings in the prior chapter.
| Python Expression | Results | Description |
|---|---|---|
| len([1, 2, 3]) | 3 | Length |
| [1, 2, 3] + [4, 5, 6] | [1, 2, 3, 4, 5, 6] | Concatenation |
| ['Hi!'] * 4 | ['Hi!', 'Hi!', 'Hi!', 'Hi!'] | Repetition |
| 3 in [1, 2, 3] | True | Membership |
| for x in [1,2,3] : print (x,end = ' ') | 1 2 3 | Iteration |
Indexing, Slicing and Matrixes
Since lists are sequences, indexing and slicing work the same way for lists as they do for strings.
Assuming the following input −
L = ['C++'', 'Java', 'Python']
| Python Expression | Results | Description |
|---|---|---|
| L[2] | 'Python' | Offsets start at zero |
| L[-2] | 'Java' | Negative: count from the right |
| L[1:] | ['Java', 'Python'] | Slicing fetches sections |
Built-in List Functions and Methods
Python includes the following list functions −
| Sr.No. | Function & Description |
|---|---|
| 1 | len(list)
Gives the total length of the list. |
| 2 | max(list)
Returns item from the list with max value. |
| 3 | min(list)
Returns item from the list with min value. |
| 4 | list(seq)
Converts a tuple into list. |
Python includes the following list methods −
| Sr.No. | Methods & Description |
|---|---|
| 1 | list.append(obj)
Appends object obj to list |
| 2 | list.count(obj)
Returns count of how many times obj occurs in list |
| 3 | list.extend(seq)
Appends the contents of seq to list |
| 4 | list.index(obj)
Returns the lowest index in list that obj appears |
| 5 | list.insert(index, obj)
Inserts object obj into list at offset index |
| 6 | list.pop(obj = list[-1])
Removes and returns last object or obj from list |
| 7 | list.remove(obj)
Removes object obj from list |
| 8 | list.reverse()
Reverses objects of list in place |
| 9 | list.sort([func])
Sorts objects of list, use compare func if given |
https://www.tutorialspoint.com/python3/python_lists.htm
标签：11,index,obj,Python,list,Lists,lists,print 来源： https://www.cnblogs.com/emanlee/p/15851143.html
本站声明： 1. iCode9 技术分享网（下文简称本站）提供的所有内容，仅供技术学习、探讨和分享； 2. 关于本站的所有留言、评论、转载及引用，纯属内容发起人的个人观点，与本站观点和立场无关； 3. 关于本站的所有言论和文字，纯属内容发起人的个人观点，与本站观点和立场无关； 4. 本站文章均是网友提供，不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属；如您发现该文章侵犯了您的权益，可联系我们第一时间进行删除； 5. 本站为非盈利性的个人网站，所有内容不会用来进行牟利，也不会利用任何形式的广告来间接获益，纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。