sort Python list with two keys but only one in reverse order

Question

I was wondering what would be a Pythonic way of sorting a list of tuples by two keys whereby sorting with one (and only one) key would be in a reverse order and sorting with

Answer 1

Sometimes there is little alternative but to use a comparator function. There was a cmp argument to sorted from its introduction to 2.4, but it was removed from Python 3 in favour of the more efficient key function. In 3.2, cmp_to_key was added to functools; it creates keys from the original objects by wrapping them in an object whose comparison function is based on the cmp function. (You can see a simple definition of cmp_to_key at the end of the Sorting How-To

In your case, since lower-casing is relatively expensive, you might want to do a combination:

class case_insensitive_and_2nd_reversed:
    def __init__(self, obj, *args):
        self.first = obj[0].lower()
        self.second = obj[1]
    def __lt__(self, other):
        return self.first < other.first or self.first == other.first and other.second < self.second
    def __lt__(self, other):
        return self.first < other.first or self.first == other.first and other.second < self.second
    def __gt__(self, other):
        return self.first > other.first or self.first == other.first and other.second > self.second
    def __le__(self, other):
        return self.first < other.first or self.first == other.first and other.second <= self.second
    def __ge__(self, other):
        return self.first > other.first or self.first == other.first and other.second >= self.second
    def __eq__(self, other):
        return self.first == other.first and self.second == other.second
    def __ne__(self, other):
        return self.first != other.first and self.second != other.second

sortedList = sorted(myList, key = case_insensitive_and_2nd_reversed)