How to pass additional arguments to custom python sorting function

As Ashish points out in the comments, we first need to combine these functions, since key only accepts a single functions. If we return a sequence (list, tuple) of the function results, Python will do the right thing, only comparing later (farther right) elements if the earlier elements are equal (source).

I know of a couple ways to do this.

Using lambdas:

sortedBookList = sorted(    bookList,     key=lambda elem: (sortByName(elem),                       sortByFirstLanguage(elem, firstLanguage),                       sortByLanguages(elem, possibleLanguages)))

Using higher-order functions:

def key_combiner(*keyfuncs):  def helper(elem):    return [keyfunc(elem) for keyfunc in keyfuncs]  return helperdef sortByFirstLanguage(firstLanguage):  def helper(elem):    return elem.language == firstLanguage  # True > False  return helperdef sortByLanguages(possibleLanguages):  def helper(elem):    if elem.language in possibleLanguages:       return possibleLanguages.index(elem.language)  return helpersortedBookList = sorted(bookList,                        key=key_combiner(sortByName,                                          sortByFirstLanguage(firstLanguage),                                          sortByLanguages(possibleLanguages))

Lambdas seem cleanest to me, so that's probably what I'd use.