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Python - List - Append, Count, Extend, Index, Insert, Pop, Remove, Reverse, Sort

🐍 Advance List

List is widely used and it's functionalities are heavily useful.

Append

Adds one element at the end of the list.
Syntax
list1.append(value)
Input
l1 = [1, 2, 3]
l1.append(4)
l1
Output
[1, 2, 3, 4]
append can be used to add any datatype in a list. It can even add list inside list.
Caution: Append does not return anything. It just appends the list.

Count

.count(value) counts the number of occurrences of an element in the list.
Syntax
list1.count(value)
Input
l1 = [1, 2, 3, 4, 3]
l1.count(3)
Output
2
It returns 0 if the value is not found in the list.

Extend

.count(value) counts the number of occurrences of an element in the list.
Syntax
list1.extend(list)
Input
l1 = [1, 2, 3]
l1.extend([4, 5])
Output
[1, 2, 3, 4, 5]
If we use append, entire list will be added to the first list like one element. Extend, instead of considering a list as one element, it joins the two lists one after other. Append works in the following way.
Input
l1 = [1, 2, 3]
l1.append([4, 5])
Output
[1, 2, 3, [4, 5]]

Index

.index(value) returns the index at which the value is found.
Syntax
list1.index(value)
Input
l1 = ['one', 2, 'three']
l1.index('three')
Output
2
Returns an error - ValueError - if the value is not there in the list.

Insert

.insert(index, value) is used to add a value to the list at a specific index. That is why it takes two arguments - index and value
Syntax
list1.insert(index, value)
Input
l1 = ['one', 'three', 4]
l1.insert(1,'two')
l1
Output
['one', 'two', 'three', 4]
It moves all values after the index, one index forward.

Pop

.pop(index) is used to remove and return the value at an index.
Syntax
list1.pop(index)
Input
l1 = [1, 2, 3, 4, 5, 6]
popped_value = l1.pop(3)
popped_value
Output
4
Input
l1
Output
[1, 2, 3, 5, 6]
On popping, the value popped is returned, which can be used in cases where you want to inform which value was popped.

Remove

.remove(value) removes the first occurrence of a value
Syntax
list1.remove(value)
Input
l1 = [1, 2, 3, 4, 3, 2, 1]
l1.remove(3)
l1
Output
[1, 2, 4, 3, 2, 1]

Reverse

.reverse() reverses and updates the list
Syntax
list1.reverse()
Input
l1 = [1, 2, 3, 4]
l1.reverse()
l1
Output
[4, 3, 2, 1]

Sort

.sort() sorts a list in ascending order by number or by alphabet. If you want to sort in descending order then add reverse=True as an argument
Syntax
list1.sort(reverse = True) #reverse = True is optional
Input
l1 = [4, 2, 1, 4]
l1.sort()
l1
Output
[1, 2, 4, 4]
Input
l1 = ['a', 'c', 'd', 'c']
l1.sort(reverse = True)
l1
Output
['d', 'd', 'c', 'a']
A list with a mix of numbers and string will return an error - TypeError.
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