Javascript style dot notation for dictionary keys unpythonic?

Question

I\'ve started to use constructs like these:

class DictObj(object):
    def __init__(self):
        self.d = {}
    def __getattr__(self, m):
        return s         


        

Answer 1

It's not bad if it serves your purpose. "Practicality beats purity".

I saw such approach elserwhere (eg. in Paver), so this can be considered common need (or desire).

Answer 2

Because you ask for undesirable side-effects:

A disadvantage is that in visual editors like eclipse+pyDev, you will see many undefined variable errors on lines using the dot notation. Pydef will not be able to find such runtime "object" definitions. Whereas in the case of a normal dictionary, it knows that you are just getting a dictionary entry.

You would need to 1) ignore those errors and live with red crosses; 2) suppress those warnings on a line by line basis using #@UndefinedVariable or 3) disable undefined variable error entirely, causing you to miss real undefined variable definitions.

Answer 3

As far as I know, Python classes use dictionaries to store their attributes anyway (that's hidden from the programmer), so it looks to me that what you've done there is effectively emulate a Python class... using a python class.

Answer 4

If you're looking for an alternative that handles nested dicts:

Recursively transform a dict to instances of the desired class

import json
from collections import namedtuple


class DictTransformer():
    @classmethod
    def constantize(self, d):
        return self.transform(d, klass=namedtuple, klassname='namedtuple')

    @classmethod
    def transform(self, d, klass, klassname):
        return self._from_json(self._to_json(d), klass=klass, klassname=klassname)

    @classmethod
    def _to_json(self, d, access_method='__dict__'):
        return json.dumps(d, default=lambda o: getattr(o, access_method, str(o)))

    @classmethod
    def _from_json(self, jsonstr, klass, klassname):
        return json.loads(jsonstr, object_hook=lambda d: klass(klassname, d.keys())(*d.values()))

Ex:

constants = {
  'A': {
    'B': {
      'C': 'D'
    }
  }
}
CONSTANTS = DictTransformer.transform(d, klass=namedtuple, klassname='namedtuple')
CONSTANTS.A.B.C == 'D'

Pros:

• handles nested dicts
• can potentially generate other classes
• namedtuples provide immutability for constants

Cons:

• may not respond to .keys and .values if those are not provided on your klass (though you can sometimes mimic with ._fields and list(A.B.C))

Thoughts?

h/t to @hlzr for the original class idea

Answer 5

Don't overlook Bunch.

It is a child of dictionary and can import YAML or JSON, or convert any existing dictionary to a Bunch and vice-versa. Once "bunchify"'d, a dictionary gains dot notations without losing any other dictionary methods.

Answer 6

I like dot notation a lot better than dictionary fields personally. The reason being that it makes autocompletion work a lot better.