sorting list of tuples by arbitrary key

Question

order = [\'w\',\'x\',\'a\',\'z\']
[(object,\'a\'),(object,\'x\'),(object,\'z\'),(object,\'a\'),(object,\'w\')]

How do I sort the above list of tuples b

Answer 1

You can use sorted, and give as the key a function that returns the index of the second value of each tuple in the order list.

>>> sorted(mylist,key=lambda x: order.index(x[1]))

[('object', 'w'), ('object', 'x'), ('object', 'a'), ('object', 'a'), ('object', 'z')]

Beware, this fails whenever a value from the tuples is not present within the order list.

Edit:

In order to be a little more secure, you could use :

sorted(mylist,key=lambda x: x[1] in order and order.index(x[1]) or len(order)+1)

This will put all entries with a key that is missing from order list at the end of the resulting list.