[Python-ideas] A key parameter for heapq.merge (original) (raw)

Steven D'Aprano steve at pearwood.info
Mon Jan 9 00:46:48 CET 2012

Simon Sapin wrote:

I’m working on a patch for a key parameter. I think it can be pretty straightforward, but I’ll measure if the "no key" case becomes slower (calls to lambda x: x) At worst we can always duplicate the loop.

In my experience, it is much faster to test against None every time through the loop than to call a do-nothing function. Instead of this:

if key is None: key = lambda x: x for value in heap: do_something_with(key(value))

this is much faster:

for value in heap: if key is None: do_something_with(value) else: do_something_with(key(value))

and this is faster still:

if key is None: for value in heap: do_something_with(value) else: for value in heap: do_something_with(key(value))

YMMV; I encourage you to benchmark.

-- Steven

More information about the Python-ideas mailing list