It happens all the time.<\/p>\n
You have a python list and you want to sort the items it contains.<\/p>\n
Basically, you can either use sort<\/span> or sorted<\/span> to achieve what you want.<\/p>\n The difference between sort<\/strong> and sorted<\/strong> is that sort<\/strong> is a list method that modifies the list in place whereas sorted<\/strong> is a built-in function that creates a new list without touching the original one.<\/p>\n In this article, I will teach you how to use these functions to sort, in an ascending or descending manner, a list of numbers, strings, tuples, or literally any object.<\/p>\n I will also teach you how to define your own custom sort functions.<\/p>\n Read the whole article if you want to learn all about list sorting in Python. Otherwise, feel free to jump straight to a specific section.<\/p>\n Sorting a numerical list is a piece of cake in Python.<\/p>\n You can sort a list of numbers (integers or floats) very easily by using the sort<\/span> method.<\/p>\n Here is an example:<\/p>\n Notice that the list L<\/strong> was sorted in place. No new objects were created.<\/p>\n If you want to create a new sorted list without modifying the original one, you should use the sorted<\/span> function instead.<\/p>\n As you can notice, both sort<\/strong> and sorted<\/strong> sort items in an ascending order by default.<\/p>\n If you want to sort in a descending order, all you have to do is add the parameter reverse = True<\/span> to either the sort<\/strong> or sorted<\/strong> functions.<\/p>\n They both accept it!<\/p>\n Here is another example to show how you can use the sort<\/strong> method in a descending manner.<\/p>\n Now let’s take a look at how to sort a list of strings.<\/p>\n So what if you want to sort a list of strings instead of numbers?<\/p>\n Well, nothing really changes.<\/p>\n You can still use sort<\/strong> or sorted<\/strong>.<\/p>\n Here is an example using sort<\/strong>:<\/p>\n and you can still use the reverse<\/strong> parameter to sort in a descending order.<\/p>\n Let’s look at another example, this time using\u00a0sorted<\/strong><\/p>\n So far so good, but there is a catch.<\/p>\n Let’s see what happens when there exists uppercase letters.<\/p>\n That’s interesting. Bananas<\/span> appears before apples<\/span><\/p>\n The reason for that is because Python treats all uppercase letters to be lower than lowercase letters.<\/p>\n If that’s what you want then cool, go ahead and use it without any modifications.<\/p>\n However, most of the time you want to treat strings as case insensitive<\/em> when it comes to sorting.<\/p>\n Starting with Python 2.4, both sort<\/strong> and sorted<\/strong> added an optional key<\/span> parameter.<\/p>\n This key<\/span> parameter specifies a function that will be called on each list item before making comparisons.<\/p>\n This is indeed very helpful because now we can pass the str.lower<\/span> as the key<\/strong> parameter to the sort<\/strong> function.<\/p>\n And this will instruct the sort<\/strong> function to perform comparisons between the all-lowercase versions of the strings which is exactly what we want!<\/p>\n As you can see, now the sorting is case insensitive.<\/p>\n In fact the key<\/strong> parameter is very powerful as it allows us to define our own custom sorting functions as we will see later.<\/p>\n Before we dive in, let’s see how Python compares two tuples.<\/p>\n Tuples are compared element by element starting from the first element which is very similar to how strings are compared.<\/p>\n In other words, you start out by comparing the first elements of the tuples and if they are not equal, this is the result of the comparison.<\/p>\n If they are equal, the second items are compared and so on.<\/p>\n If this is your goal, then just use the sort<\/span> method or the sorted<\/span> function and both will work just fine.<\/p>\n But sometimes this is not really what you want.<\/p>\n For example, assume you have a list of tuples where the first element in each tuple represents a name, and the second one represents the age.<\/p>\n And we want to sort this list of tuples by age.<\/p>\n The key parameter will again come to the rescue.<\/p>\n We can define our custom sort by defining our own key function.<\/p>\n There you go!<\/p>\n You can even write a neater code if you want by using lambdas<\/a>.<\/p>\n So what about if you have a list of generic objects and you want to sort these objects based on some custom criteria.<\/p>\n The\u00a0key<\/span> parameter is your friend.<\/p>\n Let’s take an example.<\/p>\n Assume you have a User<\/span> class that looks like this<\/p>\n A simple class that has name and age attributes.<\/p>\n Let’s create some User<\/span> objects and add them to a list.<\/p>\n Now let’s say you want to sort the objects in this list alphabetically by the name<\/span> attribute.<\/p>\n Here is one way you can do that:<\/p>\n If you want to sort the objects based on the age<\/span> attribute instead, here is what you need to do:<\/p>\n And just like that, you can define any custom sort on any python object you can think of.<\/p>\n Happy sorting! \ud83d\ude42<\/p>\n Check out the Courses section!<\/a><\/p>\n\n And so much more…<\/p>\n\n
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Sorting a List of Numbers<\/h2>\n
>>> L = [15, 22.4, 8, 10, 3.14]\r\n>>> L.sort()\r\n>>> L\r\n[3.14, 8, 10, 15, 22.4]<\/code><\/pre>\n>>> L = [15, 22.4, 8, 10, 3.14]\r\n>>> sorted_list = sorted(L)\r\n>>> L\r\n[15, 22.4, 8, 10, 3.14]\r\n>>> sorted_list\r\n[3.14, 8, 10, 15, 22.4]<\/code><\/pre>\n>>> L = [15, 22.4, 8, 10, 3.14]\r\n>>> L.sort(reverse = True)\r\n>>> L\r\n[22.4, 15, 10, 8, 3.14]<\/code><\/pre>\nSorting a List of Strings<\/h2>\n
>>> L = [\"oranges\", \"apples\", \"bananas\"]\r\n>>> L.sort()\r\n>>> L\r\n['apples', 'bananas', 'oranges']<\/code><\/pre>\n>>> L = [\"oranges\", \"apples\", \"bananas\"]\r\n>>> sorted(L, reverse = True)\r\n['oranges', 'bananas', 'apples']<\/code><\/pre>\n>>> L = [\"oranges\", \"apples\", \"Bananas\"]\r\n>>> L.sort()\r\n>>> L\r\n['Bananas', 'apples', 'oranges']<\/code><\/pre>\nSo how can you sort a list of strings in a case insensitive manner?<\/h3>\n
>>> L = [\"oranges\", \"apples\", \"Bananas\"]\r\n>>> L.sort(key=str.lower)\r\n>>> L\r\n['apples', 'Bananas', 'oranges']<\/code><\/pre>\nSorting a List of Tuples<\/h2>\n
>>> (2, 4) < (4, 1) \r\nTrue \r\n>>> (2, 4) < (2, 6)\r\nTrue<\/code><\/pre>\n>>> sorted([(5, 4), (3, 3), (3, 10)])\r\n[(3, 3), (3, 10), (5, 4)]<\/code><\/pre>\nhow can you sort a list of tuples by the second element?<\/h3>\n
def custom_sort(t):\r\n return t[1]\r\n\r\nL = [(\"Alice\", 25), (\"Bob\", 20), (\"Alex\", 5)]\r\nL.sort(key=custom_sort)\r\nprint(L)\r\n\r\n# output\r\n# [('Alex', 5), ('Bob', 20), ('Alice', 25)]<\/code><\/pre>\nL = [(\"Alice\", 25), (\"Bob\", 20), (\"Alex\", 5)]\r\nL.sort(key=lambda x: x[1])\r\nprint(L)\r\n# output\r\n# [('Alex', 5), ('Bob', 20), ('Alice', 25)]<\/code><\/pre>\nSorting a List of Objects<\/h2>\n
class User:\r\n def __init__(self, name, age):\r\n self.name = name\r\n self.age = age<\/code><\/pre>\nBob = User('Bob', 20)\r\nAlice = User('Alice', 30)\r\nLeo = User('Leo', 15)\r\nL = [Bob, Alice, Leo]<\/code><\/pre>\nL.sort(key=lambda x: x.name)\r\nprint([item.name for item in L])\r\n# output: ['Alice', 'Bob', 'Leo']<\/code><\/pre>\nL.sort(key=lambda x: x.age)\r\nprint([item.name for item in L])\r\n# output: ['Leo', 'Bob', 'Alice']<\/code><\/pre>\nLearning Python?<\/h3>\n
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