Custom sort python

Question

I have a question: This is list of lists, formed by ElementTree library.

   [['word1', <Element tag at b719a4cc>], ['word2', <Element tag at b719a6cc>], ['word3', <Element tag at b719a78c>], ['word4', <Element tag at b719a82c>]]

word1..4 may contain unicode characters i.e (â,ü,ç).

I want to sort this list of lists by my custom alphabet.

I know how to sort by custom alphabet from here sorting words in python

I also know how to sort by key from here http://wiki.python.org/moin/HowTo/Sorting

The problem is that I couldn't find the way how to apply these two method to sort my "list of lists".

Answer 1

Your first link more or less solves the problem. You just need to have the lambda function only look at the first item in your list:

alphabet = "zyxwvutsrqpomnlkjihgfedcba"

new_list = sorted(inputList, key=lambda word: [alphabet.index(c) for c in word[0]])

One modification I might suggest, if you're sorting a reasonably large list, is to change the alphabet structure into a dict first, so that index lookup is faster:

alphabet_dict = dict([(x, alphabet.index(x)) for x in alphabet)
new_list = sorted(inputList, key=lambda word: [alphabet_dict[c] for c in word[0]])

Answer 2

If I'm understanding you correctly, you want to know how to apply the key sorting technique when the key should apply to an element of your object. In other words, you want to apply the key function to 'wordx', not the ['wordx', ...] element you are actually sorting. In that case, you can do this:

my_alphabet = "..."

def my_key(elem):
    word = elem[0]
    return [my_alphabet.index(c) for c in word]

my_list.sort(key=my_key)

or using the style in your first link:

my_alphabet = "..."
my_list.sort(key=lambda elem: [my_alphabet.index(c) for c in elem[0]])

Keep in mind that my_list.sort will sort in place, actually modifying your list. sorted(my_list, ...) will return a new sorted list.