dict.get(key, default) 与 dict.get(key) 或默认值

Question

Is there any difference (performance or otherwise) between the following two statements in Python?

v = my_dict.get(key, some_default)

vs

v = my_dict.get(key) or some_default

Answer 1

There is a huge difference if your value is false-y :

>>> d = {'foo': 0}
>>> d.get('foo', 'bar')
0
>>> d.get('foo') or 'bar'
'bar'

You should not use or default if your values can be false-y.

On top of that, using or adds additional bytecode; a test and jump has to be performed. Just use dict.get() , there is no advantage to using or default here.

Answer 2

There is another difference: if some_default is not a value but an expression, it must be evaluated before being passed to dict.get() , whereas with or the expression will not be evaluated if you get a truthy value out of your dictionary. For example:

v = my_dict.get(key, do_something_that_takes_a_long_time())  # function always called
v = my_dict.get(key) or do_something_that_takes_a_long_time()  # function only called if needed

So while it is true that it isn't safe to use or if your dictionary can contain falsey values, there can potentially be a performance advantage.