Sorting Lists of Dictionaries

Frequently you want to sort a list of dictionaries, based on some particular key.

For example:

   1 a = {"key1": 5 , "key2": 8, "key3": 2}
   2 b = {"key1": 7 , "key2": 4, "key3": 9}
   3 c = {"key1": 6 , "key2": 1, "key3": 1}
   4 undecorated = [a, b, c] # how do you sort this list?

There are many ways to do this. Here's the fastest way to do it, as it avoids using a custom comparison function, instead using builtin comparisons. This is the decorate-sort-undecorate pattern, or the Schwartzian transform if you're coming from Perl.

   1 sort_on = "key2"
   2 decorated = [(dict_[sort_on], dict_) for dict_ in undecorated]
   3 decorated.sort()
   4 sorted = [dict_ for (key, dict_) in l]

In case you're wondering, the variable is named dict_ because we want to have MeaningfulNames, but we don't want to shadow the dict builtin, so we append an underscore.