Using a comparator function to sort

Question

So I'm working with a few pre-existing comparators that compare certain values in two tuples and return true if the first is greater than the second, false if otherwise. Here's the code for one of them:

def cmpValue(subInfo1, subInfo2):     """     Returns True if value in (value, work) tuple subInfo1 is GREATER than     value in (value, work) tuple in subInfo2     """     # TODO...     if subInfo1[0] > subInfo2[0]:         return True     else:         return False 

Now, I have a dictionary that has numerous tuple entries of the type being compared above. I want to sort them all in reverse order, but I don't really understand how I would accomplish that. I was thinking something like:

sortedDict = sorted(subjects, key=comparator, reverse = True) 

But I don't know what to pass into the comparator because each comparator takes two arguments (subInfo1, subInfo2). I cannot change the comparator functions.

Answer 1

You're passing the comparator as the key function. You should be passing it as the cmp, wrapped in some kind of function that turns it into a proper comparator.

def make_comparator(less_than):     def compare(x, y):         if less_than(x, y):             return -1         elif less_than(y, x):             return 1         else:             return 0     return compare  sortedDict = sorted(subjects, cmp=make_comparator(cmpValue), reverse=True) 

(Although actually, you should be using key functions:

sorted(subjects, operator.itemgetter(0), reverse=True) 

Also note that sortedDict will not actually be a dict, so the name is rather confusing.)