Returning boolean if set is empty

I am struggling to find a more clean way of returning a boolean value if my set is empty at the end of my function

I take the intersection of two sets, and want to return True or False based on if the resulting set is empty.

def myfunc(a,b):
    c = a.intersection(b)
    #...return boolean here

My initial thought was to do

return c is not None

However, in my interpreter I can easily see that statement will return true if c = set([])

>>> c = set([])
>>> c is not None
True

I've also tried all of the following:

>>> c == None
False
>>> c == False
False
>>> c is None
False

Now I've read from the documentation that I can only use and, or, and not with empty sets to deduce a boolean value. So far, the only thing I can come up with is returning not not c

>>> not not c
False
>>> not c
True

I have a feeling there is a much more pythonic way to do this, by I am struggling to find it. I don't want to return the actual set to an if statement because I don't need the values, I just want to know if they intersect.

Solution 1:

not as pythonic as the other answers, but mathematics:

return len(c) == 0

As some comments wondered about the impact len(set) could have on complexity. It is O(1) as shown in the source code given it relies on a variable that tracks the usage of the set.

static Py_ssize_t
set_len(PyObject *so)
{
    return ((PySetObject *)so)->used;
}

Solution 2:

def myfunc(a,b):
    c = a.intersection(b)
    return bool(c)

bool() will do something similar to not not, but more ideomatic and clear.

Solution 3:

If you want to return True for an empty set, then I think it would be clearer to do:

return c == set()

i.e. "c is equal to an empty set".

(Or, for the other way around, return c != set()).

In my opinion, this is more explicit (though less idiomatic) than relying on Python's interpretation of an empty set as False in a boolean context.

Solution 4:

If c is a set then you can check whether it's empty by doing: return not c.

If c is empty then not c will be True.

Otherwise, if c contains any elements not c will be False.