Box: Python dictionaries with recursive dot notation access • Hacker News Board

Re: Box: Python dictionaries with recursive dot notation access

#121

Post by aidos » Sat, May 06, 2017, 10:00 AM UTC

dllthomas wrote: post #117

aidos wrote: post #112

Earlier quoted context omitted.

Wait, you choose what to put in the dict. I like being able to map from, say, db objects to internal representations. Why wouldn't you want that?!

The concern is facing something that expects a map, and not knowing how to correctly populate it.

Time has taught me to prefer lists / flat structures as arguments to functions (and in most other storage and transfer contexts). Besides, either you're passing in entities that conform to the api, or you're not. Nothing about arbitrary keys in dicts changes that.

Re: Box: Python dictionaries with recursive dot notation access

#122

Post by smoe » Sat, May 06, 2017, 6:06 PM UTC

CloudYeller wrote: post #97

smoe wrote: post #93

Earlier quoted context omitted.

I see the value in the latter for code legibility. My gripe with it is, when I'm new to a project that uses a dict implementation like that: how do I know what happens if for example `that` is missing? Does it raise AttributeError, KeyError or just return None? Personally I'd prefer a helper functions like deep_get(dict_, dotted_path[, default]) -> value You stil have to check the docs/source what exactly happens, bu…

You can get part of the way there with operator.attrgetter: NT = collections.namedtuple('NT', ['x', 'y']) nt1 = NT(1, 2) nt2 = NT(nt1, 'asdf') assert nt2.x.y == 2 get_two = operator.attrgetter('x.y') assert get_two(nt2) == 2 If you wrap the operator.attrgetter in a try/catch, you can force a default too: https://pastebin.com/bFxGr22E

I never thought much about best implementation because I only used it i think once in ten years. But afaik I used something like this, that does the job and is easy to read

  _empty = object()
  def deep_get(dct, dotted_path, default=_empty):
      for key in dotted_path.split('.'):
        try:
          dct = dct[key]
        except KeyError:
          if default is _empty:
            raise
          return default
      return dct

Re: Box: Python dictionaries with recursive dot notation access

#123

Post by staz » Sun, May 07, 2017, 1:00 PM UTC

bgschiller wrote: post #20

nathancahill wrote: post #14

This looks really nice. I might be reading the DefaultBox docs wrong, but does it support this: box.might_exist.might_exist.might_exist.desired_key where desired_key would return a default value if one of the keys doesn't exist? I find the bulk of my dict code is checking for keys before access, or using .get('', default) recursively. Gets really hairy for deeply nested dicts.

I also found myself doing that pretty often, so I wrote this: def nget(d, *ks, **kwargs): for k in ks: d = d.get(k) if d is None: return kwargs.get('default') return d >>> d = {'a': {'b': {'c': 12 }}} >>> nget(d, 'a', 'd', 'c', default='Not Found!') 'Not Found!' >>> nget(d, 'a', 'b', 'c') 12

Your implementation suffer from a bug, if the final item is None it will return the default instead of None.

A better implementation would be:

    def rget(d, *ks, **kwargs):
        for k in ks:
            if k not in d:
                return kwargs.get('default')
            d = d[k]
        return d

Re: Box: Python dictionaries with recursive dot notation access

#124

Post by johnwheeler » Tue, May 09, 2017, 3:58 PM UTC

bmh100 wrote: post #25

johnwheeler wrote: post #5

Earlier quoted context omitted.

A really good question. I haven't looked much at the code but I'd imagine still O(1) because it's just converting the keys into a different format.

But that says nothing about whether there is a constant penalty being applied.

certainly