{"id":366,"date":"2020-10-08T07:02:08","date_gmt":"2020-10-08T07:02:08","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=366"},"modified":"2025-03-26T13:58:08","modified_gmt":"2025-03-26T13:58:08","slug":"python-map-list","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-map-list\/","title":{"rendered":"How to Transform List Elements with Python map() Function"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the Python map()<\/code> function with lists.<\/p>\n\n\n\n

Introduction to the Python map() function #<\/a><\/h2>\n\n\n\n

When working with a list<\/a> (or a tuple<\/a>), you often need to transform the elements of the list and return a new list that contains the transformed element.<\/p>\n\n\n\n

Suppose, you want to double every number in the following bonuses<\/code> list:<\/p>\n\n\n

bonuses = [100<\/span>, 200<\/span>, 300<\/span>]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
bonuses = [100<\/span>, 200<\/span>, 300<\/span>]\n\nnew_bonuses = []\n\nfor<\/span> bonus in<\/span> bonuses:\n    new_bonuses.append(bonus*2<\/span>)\n\nprint(new_bonuses)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
[200<\/span>, 400<\/span>, 600<\/span>]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Python provides a nicer way to do this kind of task by using the map()<\/code> built-in function.<\/p>\n\n\n\n
The map()<\/code> function iterates over all elements in a list (or a tuple), applies a function to each, and returns a new iterator of the new elements.<\/p>\n\n\n\n
The following shows the basic syntax of the map()<\/code> function:<\/p>\n\n\n
iterator = map(fn, list)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this syntax, fn<\/code> is the name of the function that will call on each element of the list. <\/p>\n\n\n\n
Back to the previous example, to use the map()<\/code> function, you define a function that doubles a bonus first and then use the map() function as follows:<\/p>\n\n\n
def<\/span> double<\/span>(bonus)<\/span>:<\/span>\n    return<\/span> bonus * 2<\/span>\n\n\nbonuses = [100<\/span>, 200<\/span>, 300<\/span>]\n\niterator = map(double, bonuses)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
bonuses = [100<\/span>, 200<\/span>, 300<\/span>]\niterator = map(lambda<\/span> bonus: bonus*2<\/span>, bonuses)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Once you have an iterator, you can iterate over the new elements using a for<\/code> loop.<\/p>\n\n\n\n
Or you can convert an iterator to a list by using the the list()<\/code> function:<\/p>\n\n\n
bonuses = [100<\/span>, 200<\/span>, 300<\/span>]\niterator = map(lambda<\/span> bonus: bonus*2<\/span>, bonuses)\nprint(list(iterator))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Using the Python map() function with a list of strings #<\/a><\/h2>\n\n\n\n
The following example uses the map()<\/code> function to return a new list where each element is transformed into the proper case:<\/p>\n\n\n
names = ['david'<\/span>, 'peter'<\/span>, 'jenifer'<\/span>]\nnew_names = map(lambda<\/span> name: name.capitalize(), names)\nprint(list(new_names))\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
['David'<\/span>, 'Peter'<\/span>, 'Jenifer'<\/span>]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Using the Python map() function with a list of tuples #<\/a><\/h2>\n\n\n\n
Suppose that you have the following shopping cart represented as a list of tuples:<\/p>\n\n\n
carts = [['SmartPhone'<\/span>, 400<\/span>],\n         ['Tablet'<\/span>, 450<\/span>],\n         ['Laptop'<\/span>, 700<\/span>]]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And you need to calculate the tax amount for each product with a 10% tax. In addition, you need to add the tax amount to the third element of each item in the list.<\/p>\n\n\n\n
The return list should be something like this:<\/p>\n\n\n
[['SmartPhone'<\/span>, 400<\/span>, 40.0<\/span>],\n['Tablet'<\/span>, 450<\/span>, 45.0<\/span>],\n['Laptop'<\/span>, 700<\/span>, 70.0<\/span>]]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In order to do so, you can use the map()<\/code> function to create a new element of the list and add the new tax amount to each like this:<\/p>\n\n\n
carts = [['SmartPhone'<\/span>, 400<\/span>],\n         ['Tablet'<\/span>, 450<\/span>],\n         ['Laptop'<\/span>, 700<\/span>]]\n\nTAX = 0.1<\/span>\ncarts = map(lambda<\/span> item: [item[0<\/span>], item[1<\/span>], item[1<\/span>] * TAX], carts)\n\nprint(list(carts))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
[['SmartPhone', 400<\/span>, 40.0<\/span>], ['Tablet', 450<\/span>, 45.0<\/span>], ['Laptop', 700<\/span>, 70.0<\/span>]]<\/code><\/span>Code language:<\/span> JSON \/ JSON with Comments<\/span> (<\/span>json<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Or you make this code more concise by using a lambda expression<\/a> like this:<\/p>\n\n\n
In fact, you can pass any iterable<\/a> to the map()<\/code> function, not just a list or tuple.<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
To do it, you can use a for loop<\/a> to iterate over the elements, double each of them, and add it to a new list like this:<\/p>\n\n\n