Detailed explanation of Python list insert() function

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insert() can "insert" the object into the "specified position" of the list

grammar

list.insert( index, obj )

parameter

• index : (required) index position
• obj : (optional) the object to insert

Example: inserting content into a list

list1 = [1, 2, 3]

list1.insert(1, 'a')
print(list1)

output:

[1, 'a', 2, 3]

1. Insertion position

Set the "index" to specify the "position" of the object insertion . The index has some special values ​​that need to be noted.

1.1. Positive index

When the index is a "positive number" , the index starts from 0 and counts "from left to right" .

For example, if the index is 0, it will be inserted at the first position on the left; if the index is 1, it will be inserted at the second position on the left; and so on

list1 = [1, 2, 3]
list2 = [1, 2, 3]

list1.insert(0, 'a')
print(list1)
list2.insert(1, 'a')
print(list2)

output:

['a', 1, 2, 3]
[1, 'a', 2, 3]

When the index "exceeds" the "length" of the list , no error will be reported, but it will be inserted to the far right of the list

list1 = [1, 2, 3]

list1.insert(10, 'a')
print(list1)

output:

[1, 2, 3, 'a']

1.2. Negative index

When the index is a "negative number" , the index starts from 0 and counts "from right to left" .

For example, if the index is -1, it is inserted at the second position on the right; if the index is -2, it is inserted at the third position on the right; and so on

list1 = [1, 2, 3]
list2 = [1, 2, 3]

list1.insert(-1, 'a')
print(list1)
list2.insert(-2, 'a')
print(list2)

output:

[1, 2, 'a', 3]
[1, 'a', 2, 3]

When the index "exceeds" the "length" of the list , no error will be reported, but it will be inserted to the far left of the list

list1 = [1, 2, 3]

list1.insert(-10, 'a')
print(list1)

output:

['a', 1, 2, 3]

It should be noted here that 0 does not distinguish between positive and negative, and the way of negative index can only be inserted from the second position on the right, because there is already a function such as append() or extend() that is added to the end of the list by default.

2. Insert the object

The object inserted by insert() can be "any type" .

"Integer" and "String" types will be inserted as a new element

list1 = [1, 2, 3]

list1.insert(1, 'a')
print(list1)
list1.insert(1, 9)
print(list1)

output:

[1, 'a', 2, 3]
[1, 9, 'a', 2, 3]

"List" , "Yuanzu" and "dictionary" , not every element will be inserted, but the "whole" will be inserted as an element

list1 = [1, 2, 3]
list2 = [4, 5]
tuple2 = ('a', 'b')
dict2 = {
    
    'key1': 1, 'key2': 2}
str2 = 'abc'

list1.insert(1, list2)
print(list1)
list1.insert(1, tuple2)
print(list1)
list1.insert(1, dict2)
print(list1)
list1.insert(1, str2)
print(list1)

output:

[1, [4, 5], 2, 3]
[1, ('a', 'b'), [4, 5], 2, 3]
[1, {
    
    'key1': 1, 'key2': 2}, ('a', 'b'), [4, 5], 2, 3]
[1, 'abc', {
    
    'key1': 1, 'key2': 2}, ('a', 'b'), [4, 5], 2, 3]