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Python•Foundations Practice

Python - Sort Lists

Sort List Alphanumerically

List objects have a sort()

method that will sort the list alphanumerically, ascending, by default:

Example

Sort the list alphabetically:

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

print(thislist)

Example

Sort the list numerically:

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

print(thislist)

Sort Descending

Formula

To sort descending, use the keyword argument reverse = True

Example

Sort the list descending:

thislist = ["orange", "mango", "kiwi", "pineapple", "banana"]

Formula

thislist.sort(reverse = True)
print(thislist)

Example

Sort the list descending:

thislist = [100, 50, 65, 82, 23]

Formula

thislist.sort(reverse = True)
print(thislist)

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):

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)

Case Insensitive Sort

By default the sort()

method is case sensitive, resulting in all capital letters being sorted before lower case letters:

Example

Case sensitive sorting can give an unexpected result: thislist = ["banana", "Orange", "Kiwi", "cherry"] thislist.sort()

print(thislist)

Formula

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:

Example

Formula

Perform a case - insensitive sort of the list:

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

print(thislist)

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.

Example

Reverse the order of the list items: thislist = ["banana", "Orange", "Kiwi", "cherry"] thislist.reverse()

print(thislist)

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