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Python List

List Overview

Lists are used to store multiple items in a single variable. List items are ordered, changeable, and allow duplicate values. List items are indexed, the first item has index [0], the second item has index [1] etc. When we say that lists are ordered, it means that the items have a defined order, and that order will not change. If you add new items to a list, the new items will be placed at the end of the list. The list is changeable, meaning that we can change, add, and remove items in a list after it has been created. Since lists are indexed, lists can have items with the same value means duplicates are allowed

Code :

list1 = [1,2,3,4,3,1]
print(list1)

Python List looping indexing Static way

In this Example we will pass the hard coded the starting and ending limit , which is treated as Static Looping , which is not advisable

Code :

list1 = [1,2,3,4,5]
for i in range(0,5):
 print(list1[i])

Python List looping indexing Dynamic way

here using The len() function of list we can easily loop dynamic wise.

Code :

list1 = [10,20,30,40,50]
for i in range(0,len(list1)):
 print(list1[i])

Looping the list without len

The below code shows direct looping.

Code :

list1 = [10,20,22,56]
for i in list1:
 print(i)

List len() function

Code :

list1 = [10,20,30,40]
print(list1[0])
print(list1[1])
print(list1[2])
print(list1[3])

list count()

The count() is used to count the number of occurence of given value in list.

Code :

list1 = [10,20,30,40,50]
num = 10
res1 = list1.count(num)
print(res1)

Change Item Value

To change the value of a specific item, refer to the index number:

Code :

thisList = ["apple","banana","cherry"]
thisList [1] = "BlackCurrent"
print(thisList)

Change a Range of Item Values

To change the value of items within a specific range, define a list with the new values, and refer to the range of index numbers where you want to insert the new values:

Code :

thisList = ["apple","banana","cherry","orange","kiwi","mango"]
thisList[1:3] = ["blackcurrent","watermelon"]
print(thisList)

List Overview

Code :

list1 = [1,2,3,4,3,1]
print(list1)

List Append()

the append() is used to add the items last in the list

Code :

list1 = [10,20,30]
list1.append(40)
print(list1)

List insert()

To insert a list item at a specified index, use the insert() method. The insert() method inserts an item at the specified index:

Code :

thisList = [1,2,3]
thisList.insert(1,7)
print(thisList)

List remove()

The remove() method removes the specified item. if duplicate items is there it will only delete the first occurence

Code :

thisList = [7,9,10]
thisList.remove(10)
print(thisList)

List del()

del() with take the parameter as index and delete the value from list for specified position.

Code :

list1 = [1,2,3,4,3,1]
del list1[0]
print(list1)

List sort()

The sort() is used to sort the list in ascending and descending order

Code :

list1 = [1,5,4,7,9]
list1.sort()

List copy()

You cannot copy a list simply by typing l2 = l1, because: l2 here only be a reference to l1, and changes done in l1 will automatically also be made in l2. There are ways to make a copy, one way is to use the built-in List method copy().

Code :

l1 = [10,20,30,40]
res1 = l1.copy()
print(res1)

Join Two Lists using '+' operators

Using ‘+’ operator we can concate two lists.

Code :

list1 = [10,20,30]
list2 = [55,44,66]
res1 = list1 + list2
print(res1)

Join Two Lists using extends Function

Use the extend() method to add list2 at the end of list1:

Code :

list1 = [7,8,9]
list2 = [1,2,3]
list1.extend(list2)
print(list1)

List reverse()

Code :

list1 = [1,2,3,4,3]
list1.reverse()
print(list1)