Python list(List)

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

Python has 6 built-in types for sequences, but the most common ones are lists and tuples.

Operations that can be performed on sequences include indexing, slicing, adding, multiplying, and checking members.

In addition, Python has built-in methods for determining the length of a sequence and determining the largest and smallest elements.

List is the most commonly used Python data type, which can appear as a comma-separated value within square brackets.

The data items of the list do not need to be of the same type

To create a list, just enclose the different data items separated by commas in square brackets. As shown below:

list1 = ['physics', 'chemistry', 1997, 2000];

list2 = [1, 2, 3, 4, 5];

list3 = ["a" , "b", "c", "d"];

The same as the index of the string, the list index starts from 0. Lists can be intercepted, combined, etc.

Access the values ​​in the list

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

#!/usr/bin/python

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]

The output result of the above example:

list1[0]: physics

list2[1:5]: [2, 3, 4, 5]

Update list

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

#!/usr/bin/python

list = ['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 the use of the append() method in the next chapter

The above example output result:

Value available at index 2:

1997

New value available at index 2:

2001

Delete list elements

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

#!/usr/bin/python

list1 =[ 'physics', 'chemistry', 1997, 2000];

print list1;

del list1[2];

print "After deleting value at index 2 : "

print list1;

The output result of the above example:

['physics', 'chemistry', 1997, 2000]

After deleting value at index 2 :

['physics', 'chemistry', 2000]

Note: We will discuss the use of the remove() method in the next chapter

Python list script operators

The + and * operators for lists are similar to strings. The + sign is used for combined lists, and the * sign is used for repeated lists.

looks like this:

Python expression

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!'] Repeat

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 interception

Python list interception and string The operation type is as follows:

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

Operation:

Python expression

result

Description

L[2] 'SPAM!' Read the third element in the list

L[-2] 'Spam' Read the second to last element in the list

L[1:] ['Spam', 'SPAM!'] Intercept the list starting from the second element

Python list functions & methods

Python includes the following functions:

Serial number

Function

1 cmp(list1, list2)
Compare the elements of two lists

2 len(list)
The number of list elements

3 max(list)
Return the maximum value of the list elements

4 min(list)
Return the list elements Minimum value

5 list(seq)
Convert tuple to list

Python contains 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 ​​from another sequence at the end of the list at once (extend the original with a new list list)

4 ​​list.index(obj)
Find the index position of the first matching item of a value from the list

5 list.insert(index, obj)
Insert the object into the list

6 list. pop([index])
Removes an element in the list (the last element by default) and returns the value of the element

7 list.remove(obj)
Removes the first match of a value in the list

8 list.reverse()
reverse the elements in the list

9 list.sort([func])
sort the original list