python: arbitrary order by

Question

In Oracle SQL there is a feature to order as follow:

order by decode("carrot" = 2
               ,"banana" = 1
               ,"apple" = 3)

What is the best way to implement this in python?

I want to be able to order a dict by its keys. And that order isn't necessarily alphabetically or anything - I determine the order.

Answer 1

Use the key named keyword argument of sorted().

#set up the order you want the keys to appear here
order = ["banana", "carrot", "apple"]

# this uses the order list to sort the actual keys.
sorted(keys, key=order.index)

For higher performance than list.index, you could use dict.get instead.

#this builds a dictionary to lookup the desired ordering
order = dict((key, idx) for idx, key in enumerate(["banana", "carrot", "apple"]))

# this uses the order dict to sort the actual keys.
sorted(keys, key=order.get)