Master Python list.sort vs sorted: Tips, Syntax, and Real-World Examples

Overall, sort modifies the original list, while sorted returns a new sorted object. list.sort() is slightly faster than sorted(iter).

1. The sort() Method

sort() sorts the list in place; it can accept optional parameters to define the sorting behavior. Only mutable sequences like lists can be sorted, not tuples.

Syntax

list.sort(cmp=None, key=None, reverse=False)
# cmp parameter existed in Python 2.0
# removed in Python 3.0

Parameters

cmp – optional custom comparison function (Python 2 only) key – function that extracts a comparison key from each element reverse – sort order (True for descending, False for ascending, default)

reverse=True – descending

reverse=False – ascending (default)

The method sorts the original list in place and returns None.

Examples

# 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)
aList  # [6, 5, 4, 3, 2, 1]

# Sort by a specific element (second element of tuple)
def takeSecond(elem):
    return elem[1]

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

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

# Custom comparison function (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 order (Python 2)

Other Tips

To obtain a sorted copy while keeping the original list unchanged, use either slicing with sorted or the list.copy() method.

# Method 1: copy then sort
aList = [5, 4, 1, 3, 6, 2]
bList = aList[:]  # deep copy
bList.sort()
print(aList)  # [5, 4, 1, 3, 6, 2]
print(bList)  # [1, 2, 3, 4, 5, 6]

# Method 2: use sorted
aList = [5, 4, 1, 3, 6, 2]
bList = sorted(aList)  # [1, 2, 3, 4, 5, 6]

Copying via slicing creates a new list; simple assignment would reference the same list.

2. The sorted() Function

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

Syntax

sorted(iterable, key=None, reverse=False)

Parameters

iterable – the collection to sort key – function to extract a comparison key from each element reverse – sort order (True for descending, False for ascending)

The function returns a new list containing the sorted items.

Examples

# Default ascending sort
a = [5, 2, 3, 1, 4]
sorted(a)  # [1, 2, 3, 4, 5]

# Sorting a dictionary's 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]))

Other Example

# Medal ranking example
s = "Germany 10 11 16
Italy 10 10 20
Netherlands 10 12 14
France 10 12 11
UK 22 21 22
China 38 32 18
Japan 27 14 17
USA 39 41 33
ROC 20 28 23
Australia 17 7 22
Hungary 6 7 7
Canada 7 6 11
Cuba 7 3 5
Brazil 7 6 8
New Zealand 7 6 7"
stodata = s.split('
', -1)
para = {}
for line in range(len(stodata)):
    data = stodata[line].split(' ')
    print(data)
    para[data[0]] = [int(i) for i in data[1:]]

new_para = sorted(para.items(), key=lambda x: (x[1], x[0]))