When providing a custom comparator, it should generally return an integer/float value that follows the following pattern (as with most other programming languages and frameworks): We need to pay attention to the fact that in Python 3 the parameter name and semantics have changed. Generally, you want to use the built-in sorted() function which takes a custom comparator as its parameter. Since the OP was asking for using a custom compare function (and this is what led me to this question as well), I want to give a solid answer here:

In the chain that creates the original list one function didn't return anything but the return value was used. How can I sort this lists with a custom function? I have no idea why that is, coming from mostly C++ this contradicts any idea of a callback function for me.

But in any case the functions don't get a list as an argument but a None. Or sorted(mylist, cmp=lambda x,y: compare(x,y))Īlso I tried list.sort() with the same parameters. Or sorted(mylist, cmp=compare, key=fitness) Then I tried to call them by: sorted(mylist, cmp=compare) I created two functions, compare and fitness: def compare(item1, item2): This function calculates the fitness of the list by which the elements shall be sorted. I want to sort this list by applying a custom compare function to each element. I have a list of lists, 50 times 5 elements. I know there are several questions named like this, but they don't seem to work for me.

Sorting python list of dictionaries