Set Comprehension And Different Comparable Relations

I have set objects which are comparable in some way and I want to remove objects from the set. I thought about how this problem changes, for different comparable relations between

Solution 1:

I will precede with confirming your claim - changing set while iterating it would trigger a RuntimeError, which would claim something along the lines of "Set changed size during iteration".

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Now, lets start from the compare function: since you are using sets, x is y is probably like x == y and the last one is always a better choice when possible.

Furthermore, no need for the condition; you are already performing one:

defcompare(x, y):
    return x != y and x % y == 0

Now to the set comprehension - that's a messy one. After setting the set as an argument - which is better than using global variable - the normal code would be something like

forxin my_set:
    foryin my_set:
        ifcompare(x, y):
            forain (x, y):
                temp.append(a)

notice the last two lines, which do not use unpacking because that would be impossible in the comprehension. Now, all what's left is to move the a to the front and make all : disappear - and the magic happens:

def list_solution (my_set):
    return my_set - {a for x in my_set for y in my_set if compare(x, y) for a in (x, y)}

you can test it with something like

my_set = set([4, 2, 3, 7, 9, 16])
print(list_solution(my_set)) # {7}

• The condition and the iteration on (x, y) can switch places - but I believe that iterating after confirming would be faster then going in and starting to iterate when there's a chance you wouldn't perform any action.

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The change for the second case is minor - merely using x instead of the x, y unpacking:

def list_solution_2 (my_set):
    return my_set - {x for x in my_set for y in my_set if compare(x, y)}