Sort dict’s keys by values

Can we actually sort a Python’s dict? No, but we can sort a list that contains its keys and values.

A simplest way to do this is to use a sort method:

>>> d = {'c': 100, 'a': 0, 'b': 10}
>>> items = d.items()
>>> items.sort(lambda x, y: cmp(x[1], y[1]))
>>> items
[('a', 0), ('b', 10), ('c', 100)]

We can use a key argument to make function call a bit shorter:

>>> items = d.items()
>>> items.sort(key=lambda i: i[1])
>>> items
[('a', 0), ('b', 10), ('c', 100)]

Also we can use a sorted built-in:

>>> sorted(d.iteritems(), key=lambda i: i[1])
[('a', 0), ('b', 10), ('c', 100)]

But what if we care about speed? According to Gregg Lind, the fastest solution uses operator.itemgetter (that is suggested in PEP 265 named “Sorting Dictionaries by Value”) instead of lambda function:

>>> from operator import itemgetter
>>> sorted(d.iteritems(), key=itemgetter(1))
[('a', 0), ('b', 10), ('c', 100)]

This version is 10x faster than first three.