The **`sort()` function** is a member of the [list](https://www.educative.io/answers/what-is-a-python-list) data structure in Python. By default, it sorts the elements of a list in ascending order. 

list = [20, 5, -10, 300]
list.sort()
print(list)

In the case of strings and characters, sorting is done based on their ASCII values.

# Sorting
The Python list `sort()` has been using the **Timsort** algorithm since version 2.3. 


This algorithm has a runtime complexity of *O(n.logn)*.


The function has two optional attributes which can be used to specify a customized sort:

The `key` attribute requires a callable function as its input. The function will specify the sorting criteria.


list1 = [20, 5, -10, 300]
list1.sort(reverse=True) # Sort the list in descending order

# A callable function which returns the length of a string
def lengthKey(str):
  return len(str)

list2 = ["London", "Paris", "Copenhagen", "Melbourne"]
# Sort based on the length of the elements
list2.sort(key=lengthKey)
print(list2)

What is the Python list sort()?

Python's `sort()` function sorts lists in ascending order by default, utilizing Timsort algorithm with O(n log n) complexity. Optional `key` attribute customizes sorting.