4 ms·

Personally think, ruby got it right where we can pass a lambda with the `key` parameter.

• orf 5y ago
  You can with Python, it accepts any callable
  • BWStearns 5y ago
    I think they're pointing out that the callable should be given the key value. So like, let's say a missing key should be assigned its own value by default. Below I try to do that but the callable doesn't seem to be passed the key. ``` In [22]: foo = defaultdict(lambda k: k) In [23]: foo[1] --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-23-5a39798fc62e> in <module> ----> 1 foo[1] TypeError: <lambda>() missing 1 required positional argument: 'k' ``` I could envision this being useful for using a defaultdict as something like a local cache for something where requests are expensive. Below is how one might want to use it but it'll fail because the lambda is not given the key argument. ``` profiles = defaultdict(lambda p_id: get_profile_from_site(p_id)) ```