Python List sort()

The list's sort() method sorts the elements of a list.

prime_numbers = [11, 3, 7, 5, 2]

# sort the list in ascending order
prime_numbers.sort()

print(prime_numbers)

# Output: [2, 3, 5, 7, 11]

sort() Syntax

numbers.sort(reverse, key)

The sort() method can take two optional keyword arguments:

• reverse - By default False. If True is passed, the list is sorted in descending order.
• key - Comparion is based on this function.

Sort in Descending order

We can sort a list in descending order by setting reverse to True.

numbers = [7, 3, 11, 2, 5]

# reverse is set to True
numbers.sort(reverse = True)

print(numbers)

Output

[11, 7, 5, 3, 2]

Sort a List of Strings

The sort() method sorts a list of strings in dictionary order.

cities = ["Tokyo", "London", "Washington D.C"]

# sort in dictionary order
cities.sort()
print(f"Dictionary order: {cities}")

# sort in reverse dictionary order
cities.sort(reverse = True)
print(f"Reverse dictionary order: {cities}")

Output

Dictionary order: ['London', 'Tokyo', 'Washington D.C']
Reverse dictionary order: ['Washington D.C', 'Tokyo', 'London']

Reverse Strings Based on Length

The sort() method can sort items based on a function. For example,

text = ["abc", "wxyz", "gh", "a"]

# stort strings based on their length
text.sort(key = len)
print(text)

Output

['a', 'gh', 'abc', 'wxyz']

len is a built-in function that returns the length of a string.

Since we passed the len function as key, the strings are sorted based on their length.