Python's dict has a
get method. It'll either return an existing value for a given key or return a default value if the key is not in the dict. It's very tempting to write code like
val = d.get(key, Object()), however you need to think about the performance implications. Since function arguments are evaluated before calling the function, this means the a new
Object will be created regardless if it's in the dict or not. Let's see this affects performance.
get_default will create new
Point every time and
get_none will create only if there's no such object, it works since
or evaluate it's arguments lazily and will stop once the first one is
True.
First we'll try with a missing key:
In [1]: %run default_vs_none.py
In [2]: locations = {} # name -> Location
In [3]: %timeit get_default(locations, 'carmen')
384 ns ± 2.56 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [4]: %timeit get_none(locations, 'carmen')
394 ns ± 1.61 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
Not so much difference. However if the key exists:
In [5]: locations['carmen'] = Location(7, 3)
In [6]: %timeit get_default(locations, 'carmen')
377 ns ± 1.84 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [7]: %timeit get_none(locations, 'carmen')
135 ns ± 0.108 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
We get much faster results.
