I'd like to propose an addition to `dict` but I'm not necessarily proposing
what's written here as the API. When I initially saw the need for this
myself, I hastily wrote it as:
def setdefault_call(a_dict, key, default_func):
try:
return a_dict[key]
except KeyError:
default = default_func()
a_dict[key] = default
return default
If its not clear, the purpose is to eliminate the overhead of creating an
empty list or similar in situations like this:
d = {}
for i in range(1000000): # some large loop
l = d.setdefault(somekey, [])
l.append(somevalue)
# instead...
for i in range(1000000):
l = d.setdefault_call(somekey, list)
l.append(somevalue)
One potential drawback I see to the concept is that I think there will be a
need to explicitly say "no arguments can get passed into this call".
Otherwise users may defeat the purpose with constructions like this:
d.setdefault_call("foo", list, ["default value"])
I'd mainly like feedback on this concept overall, and if its liked, perhaps
an API discussion to follow. Thanks!
PS
Other APIs I've considered for this are a new keyword argument to the
existing `setdefault()`, or perhaps more radically for Python, a new
keyword argument to the `dict()` constructor that would get called as an
implicit default for `setdefault()` and perhaps used in other scenarios
(essentially defining a type for dict values).
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