Master Python’s sort vs sorted: When and How to Use Each Efficiently

Overall, sort is a method applied to lists that modifies the original list, while the built‑in function sorted can sort any iterable and returns a new object. list.sort() is slightly faster than sorted(iterable).

1. sort function

list.sort() sorts the list in place; it can accept optional arguments to control the sorting behavior. Lists are mutable, tuples cannot be sorted in place.

Syntax

<code>list.sort(cmp=None, key=None, reverse=False)
# cmp argument existed in Python 2, removed in 3.0</code>

Parameters

cmp – optional custom comparison function (Python 2 only). key – function that extracts a comparison key from each element. reverse – if True, sort in descending order.

reverse=True – descending

reverse=False – ascending (default)

Examples

<code># Ascending
aList = [5, 4, 1, 3, 6, 2]
aList.sort()  # [1, 2, 3, 4, 5, 6]

# Descending
aList = [5, 4, 1, 3, 6, 2]
aList.sort(reverse=True)  # [6, 5, 4, 3, 2, 1]

# Sort by second element
def takeSecond(elem):
    return elem[1]

random = [(2, 2), (3, 4), (4, 1), (1, 3)]
random.sort(key=takeSecond)  # [(4, 1), (2, 2), (1, 3), (3, 4)]

# Sort by length
x = ['a', 'bbb', 'cc']
x.sort(key=len)  # ['a', 'cc', 'bbb']

# Custom comparison (Python 2 only)
def comp(x, y):
    if x < y:
        return 1
    elif x > y:
        return -1
    else:
        return 0

aList = [5, 4, 1, 3, 6, 2]
aList.sort(comp)  # descending in Python 2</code>

Other tips

To keep the original list unchanged, create a copy and sort the copy, or use the sorted() function which returns a new sorted list.

<code># Method 1 – copy then sort
aList = [5, 4, 1, 3, 6, 2]
bList = aList[:]  # deep copy
bList.sort()
# bList is [1, 2, 3, 4, 5, 6]

# Method 2 – use sorted
bList = sorted(aList)  # [1, 2, 3, 4, 5, 6]</code>

2. sorted function

sorted() can sort any iterable and returns a new list.

Syntax

<code>sorted(iterable, key=None, reverse=False)</code>

Parameters

iterable – the collection to sort. key – function that extracts a comparison key from each element. reverse – if True, sort in descending order.

Examples

<code># Simple list
a = [5, 2, 3, 1, 4]
sorted(a)  # [1, 2, 3, 4, 5]

# Dictionary keys
b = {1: 'D', 2: 'B', 3: 'B', 4: 'E', 5: 'A'}
sorted(b)  # [1, 2, 3, 4, 5]

# Sort dictionary items by key
sorted(b.items(), key=lambda x: x[0])

# Sort dictionary items by value length
sorted(b.items(), key=lambda x: len(x[1]))
</code>