Python list (Lists)

Python list (Lists)
Python list (Lists)

Sequence is the most basic data structure in Python. Each element in the sequence is assigned a number-its location, or index. The first index is 0, the second index is 1, and so on.

Python has six built-in sequence types, but the most common is list and metadata.

Operations that can be performed by sequences include indexing, slicing, adding, multiplication, and checking members.

In addition, Python has built-in methods to determine the sequence length and the maximum and minimum elements.

A list is the most common Python data type. It can appear as a comma-separated value in square brackets.

List data items do not need to have the same type

To create a list, you only need to enclose different data items separated by commas (,) in square brackets. As follows:

list1 = ['physics', 'chemistry', 1997, 2000];list2 = [1, 2, 3, 4, 5 ];list3 = ["a", "b", "c", "d"];

Like the string index, the List Index starts from 0. The list can be intercepted and combined.

Value in the access list

Use subscript indexes to access values in the list. You can also use square brackets to intercept characters, as shown below:

#!/usr/bin/pythonlist1 = ['physics', 'chemistry', 1997, 2000];list2 = [1, 2, 3, 4, 5, 6, 7 ];print "list1[0]: ", list1[0]print "list2[1:5]: ", list2[1:5]

Output result of the above instance:

list1[0]:  physicslist2[1:5]:  [2, 3, 4, 5]

To update the list, you can modify or update the data items in the list. You can also use the append () method to add the list items, as shown below:

#!/usr/bin/pythonlist = ['physics', 'chemistry', 1997, 2000];print "Value available at index 2 : "print list[2];list[2] = 2001;print "New value available at index 2 : "print list[2];

Note: we will discuss how to use the append () method in the following sections.

Output result of the above instance:

Value available at index 2 :1997New value available at index 2 :2001

Delete list elements

You can use the del statement to delete the list elements, as shown in the following example:

#!/usr/bin/pythonlist1 = ['physics', 'chemistry', 1997, 2000];print list1;del list1[2];print "After deleting value at index 2 : "print list1;

Output result of the above instance:

['physics', 'chemistry', 1997, 2000]After deleting value at index 2 :['physics', 'chemistry', 2000]

Note: we will discuss how to use the remove () method in the following sections.

Python list script Operator

The operators of list pairs + and * are similar to strings. + Is used to combine the list, and * is used to repeat the list.

As follows:

Python expressions	Result	Description
Len ([1, 2, 3])	3	Length
[1, 2, 3] + [4, 5, 6]	[1, 2, 3, 4, 5, 6]	Combination
['Hi! '] * 4	['Hi! ', 'Hi! ', 'Hi! ', 'Hi! ']	Repeated
3 in [1, 2, 3]	True	Whether the element exists in the list
For x in [1, 2, 3]: print x,	1 2 3	Iteration

Python list Truncation

The list truncation and string operation types of Python are as follows:

L = ['spam', 'Spam', 'SPAM!']

Operation:

Python expressions	Result	Description
L [2]	'Spam! '	Reads the third element from the list.
L [-2]	'Spam'	Reads the second-to-last element from the list.
L [1:]	['Spam', 'spam! ']	Truncates the list from the second element.

Python list Functions & Methods

Python includes the following functions:

Serial number	Function
1	Cmp (list1, list2) Compare two list elements
2	Len (list) Number of list elements
3	Max (list) Returns the maximum value of the list element.
4	Min (list) Returns the minimum value of the list element.
5	List (seq) Convert tuples to a list

Python includes the following methods:

Serial number	Method
1	List. append (obj) Add a new object at the end of the list
2	List. count (obj) Count the number of times an element appears in the list
3	List. extend (seq) Append multiple values in another sequence at the end of the list (extend the original list with the new list)
4	List. index (obj) Locate the index location of the first matching item of a value from the list
5	List. insert (index, obj) Insert objects to the list
6	List. pop (obj = list [-1]) Removes an element from the list (the last element by default) and returns the value of this element.
7	List. remove (obj) Removes the first matching item of a value from the list.
8	List. reverse () Elements in the reverse list
9	List. sort ([func]) Sort the original list