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Python Lists

Lists are used to store multiple items in a single variable. They are just like dynamically sized arrays, declared in other languages (vector in C++ and ArrayList in Java). Lists need not be homogeneous always which makes it the most powerful tool in Python

List Creation

List created by declare all the items inside the square brackets []

#List Creation
languages = ["Python", "Java", "Javascript"]
print(type(languages))

#Multiple data types can store in list
user_details = [1, "PYTHON", "99.0", ["Jan", "Feb"]]
print(user_details)

Output

<class 'list'>
[1, 'PYTHON', '99.0', ['Jan', 'Feb']]

List Reading

List items can be read with the help of positive or negative index of that corresponding position

"Jan" "Feb" "Mar" "Apr" "May" "Jun"
0 1 2 3 4 5
-6 -5 -4 -3 -2 -1

Every item in the list have both positive and negative index like the above table

#List Reading
month_list = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]

#Reading the first item of the list
print(month_list[0])
print(month_list[-6])

#Reading the second item of the list
print(month_list[1])
print(month_list[-5])

#Reading the last item of the list
print(month_list[5])
print(month_list[-1])

Output

Jan
Jan
Feb
Feb
Jun
Jun

List Update

List are mutable data types in python, so we can perform the update operation. No need to create new object for modification

#List Update
month_list = ["Jan", "Dec", "Mar", "Apr", "May", "Jun"]
print(id(month_list))

#Update using index of the item
month_list[1] = "Feb"
print(month_list)
print(id(month_list))

Output

140324018130432
['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun']
140324018130432

List Deletion

Since list are mutable data types in python, we can perform the delete operation without delete the entire object and recreate for the few deletion

#List Deletion
month_list = ["Jan", "Dec", "Feb", "Mar", "Apr", "May", "Jun"]
print(id(month_list))

#Deletion using index of the item
month_list.remove("Dec")
print(month_list)
print(id(month_list))

Output

139779868761664
['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun']
139779868761664

Since list is immutable data type, id of the list object not changed even after deletion

List Slicing

List slicing helps to return the required objects from the given list

ListName(start Index: stop Index: step Value (optional)]

  • start Index Not declare means, first value index consider by python

  • stop Index Not declare means, last value index consider by python

Read a object with the help of positive and negative index value

"Jan" "Feb" "Mar" "Apr" "May" "Jun"
0 1 2 3 4 5
-6 -5 -4 -3 -2 -1 
#List Slicing
month_list = ["Jan", "Feb", "Mar", "Apr", "May", "Jun"]

#Print the first two items
print(month_list[0:2])
print(month_list[-6:2])
print(month_list[:2])

#Print the middle two items
print(month_list[2:4])
print(month_list[-4:4])

#Print the last two items
print(month_list[4:6])
print(month_list[-2:6])
print(month_list[4:])

Output

['Jan', 'Feb']
['Jan', 'Feb']
['Jan', 'Feb']
['Mar', 'Apr']
['Mar', 'Apr']
['May', 'Jun']
['May', 'Jun']
['May', 'Jun']