Built-in Sort in Python

Main Idea

• list.sort(): method defined for list, modifies the list in-place (returns None)
• sorted(): built-in function, builds a new sorted list from an iterable (e.g. string -> list of characters, dict -> list of dictionary keys)

* both sorts are stable

• example: sort v.s. sorted

  >>> 'acb'.sort()
  Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  AttributeError: 'str' object has no attribute 'sort'
  >>> sorted('acb')
  ['a', 'b', 'c']
  

• caution: when using dictionary as an iterable

  >>> scores = {'Alice': 90, 'Carl': 95, 'Bob': 80}                                                                  
  >>> list(scores)                                                                                                   
  ['Alice', 'Carl', 'Bob']
  >>> for name in scores: # equivalent to scores.keys()
  ...     print(name)
  ... 
  Alice
  Carl
  Bob
  >>> sorted(scores)                                                                                      
  ['Alice', 'Bob', 'Carl']
  

Arguments

• key: function to be called on each element, e.g. str.lower, lambda x: x.attribute
• reverse: False (default) - Ascending, True - Descending

>>> sorted(scores, key=lambda x: scores[x], reverse=True)
['Carl', 'Alice', 'Bob']

>>> nums = [5, 9, 2, 6]
>>> sorted(range(len(nums)), key=lambda k: nums[k])
[2, 0, 3, 1]

Reference: https://wiki.python.org/moin/HowTo/Sorting

Relevant:

1. LeetCode 1366. Rank Teams by Votes