Runtime difference between set.discard and set.remove methods in Python?

Question

The official Python 2.7 docs for these methods sounds nearly identical, with the sole difference seeming to be that remove() raises a KeyError while discard does not.

<

Answer 1

Raising an exception in one case is a pretty meaningful difference. If trying to remove an element from a set that is not there would be an error, you better use set.remove() rather than set.discard().

The two methods are identical in implementation, except that compared to set_discard() the set_remove() function adds the lines:

if (rv == DISCARD_NOTFOUND) {
    set_key_error(key);
    return NULL;
}

This raises the KeyError. As this is slightly more work, set.remove() is a teeniest fraction slower; your CPU has to do one extra test before returning. But if your algorithm depends on the exception then the extra branching test is hardly going to matter.