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8.0 Python: Sort Lists

8.1 Sort List Alphanumerically​

List objects have a sort() method that will sort the list alphanumerically, ascending, by default:

8.1.1 Example​

Sort the list alphabetically:

thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort()
print(thislist)

8.1.2 Example​

Sort the list numerically:

thislist = [100, 50, 65, 82, 23]
thislist.sort()
print(thislist)

8.2 Sort Descending​

To sort descending, use the keyword argument reverse = True:

8.2.1 Example​

Sort the list descending:

thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]
thislist.sort(reverse = True)
print(thislist)

8.2.2 Example​

Sort the list descending:

thislist = [100, 50, 65, 82, 23]
thislist.sort(reverse = True)
print(thislist)

8.3 Customize Sort Function​

You can also customize your own function by using the keyword argument key = function.

The function will return a number that will be used to sort the list (the lowest number first):

8.3.1 Example​

Sort the list based on how close the number is to 50:

def myfunc(n):
  return abs(n - 50)

thislist = [100, 50, 65, 82, 23]
thislist.sort(key = myfunc)
print(thislist)

8.4 Case Insensitive Sort​

By default the sort() method is case sensitive, resulting in all capital letters being sorted before lower case letters:

8.4.1 Example​

Case sensitive sorting can give an unexpected result:

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort()
print(thislist)

Luckily we can use built-in functions as key functions when sorting a list.

So if you want a case-insensitive sort function, use str.lower as a key function:

8.4.2 Example​

Perform a case-insensitive sort of the list:

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.sort(key = str.lower)
print(thislist)

8.5 Reverse Order​

What if you want to reverse the order of a list, regardless of the alphabet?

The reverse() method reverses the current sorting order of the elements.

8.5.1 Example​

Reverse the order of the list items:

thislist = ["banana", "Orange", "Kiwi", "cherry"]
thislist.reverse()
print(thislist)