How to sort a Python list

Suppose that you have a Python list,

[1, 4, 3, 7, 2, 12, -3, 3]

that needed to be sorted.

The list can be sorted by directly applying the sort() method to the list, and indirectly by using the sorted().

Using sort()

The list will be sorted and the list will now become the new sorted list.

>>> y = [1, 4, 3, 7, 2, 12, -3, 3]
>>> y.sort()
>>> y
[-3, 1, 2, 3, 3, 4, 7, 12]

Using sorted()

The list will be sorted as a new list.

We can create a new sorted list, and the original remains.

>>> y = [1, 4, 3, 7, 2, 12, -3, 3]
>>> sorted(y)
[-3, 1, 2, 3, 3, 4, 7, 12]
>>> y
[1, 4, 3, 7, 2, 12, -3, 3]

How to sort Python dictionary

To sort a Python dictionary, and append the keys into a list.

>>> x = {'a': 2, 'c': 1, 'b': 3}
>>> sorted(x, key=x.get)
['c', 'a', 'b']

To sort a Python dictionary, and append tuples of the key and value into a list.

>>> x = {'a': 2, 'c': 1, 'b': 3}
>>> [(the_key, x[the_key]) for the_key in sorted(x, key=x.get)]
[('c', 1), ('a', 2), ('b', 3)]

To sort a Python dictionary, and append the keys into a tuple, and the values into a tuple.

>>> x = {'a': 2, 'c': 1, 'b': 3}
>>> [(the_key, x[the_key]) for the_key in sorted(x, key=x.get)]
[('c', 1), ('a', 2), ('b', 3)]
>>> x = {'a': 2, 'c': 1, 'b': 3}
>>> the_keys, the_vals = zip(*[(the_key, x[the_key])
for the_key in sorted(x, key=x.get)])
>>> the_keys
('c', 'a', 'b')
>>> the_vals
(1, 2, 3)

The results from the above examples are in ascending order. To sort in descending order, attach reverse=True at the end of the sorted() function.

>>> x = {'a': 2, 'c': 1, 'b': 3}
>>> sorted(x, key=x.get, reverse=True)
['b', 'a', 'c']

Sort Python dictionary

Suppose that mydict is a dictionary defined by

mydict = {'a': 2, 'c': 5, 'b': 1, 'd': 4}

Remember that dictionary has no function sort, since it is unordered, not like a list, or tuple.

However, the key function, introduced in version 2.4, is helpful in sorting a dictionary.

To sort by items, and return the keys and items,

sorted( mydict.items(), key=lambda x: x[1] )

output:

[('b', 1), ('a', 2), ('d', 4), ('c', 5)]

To return only the keys, sorted by the items,

sorted( mydict.keys(), key=lambda x: mydict[x] )

output:

['b', 'a', 'd', 'c']

Note that, adding reverse=True at the end of the sorted function would produce a decending order list.

sorted( mydict.items(), key=lambda x: x[1] )

output:

[('c', 5), ('d', 4), ('a', 2), ('b', 1)]

Happy sorting.