I've seen this pattern a lot at a past employer, and despite the obvious convenience I've come to see it as an anti-pattern: for people expecting Python semantics it's quite surprising to read code that writes foo.bar and then reads back foo['bar']. We should not try to import JavaScript's object model into Python.

On Tue, Apr 14, 2020 at 8:06 PM Raymond Hettinger <raymond.hettinger@gmail.com> wrote:
SimpleNamespace() is really good at giving attribute style-access. I would like to make that functionality available to the JSON module (or just about anything else that accepts a custom dict) by adding the magic methods for mappings so that this works:

     catalog = json.load(f, object_hook=SimpleNamespace)
     print(catalog['clothing']['mens']['shoes']['extra_wide']['quantity'])      # currently possible with dict()
     print(catalog.clothing.mens.shoes.extra_wide.quantity])                 # proposed with SimpleNamespace()
     print(catalog.clothing.boys['3t'].tops.quantity                                   # would also be supported

I've already seen something like this in production; however, people are having to write custom subclasses to do it.  This is kind of bummer because the custom subclasses are a pain to write, are non-standard, and are generally somewhat slow.  I would like to see a high-quality version this made more broadly available.

The core idea is keep the simple attribute access but make it easier to load data programmatically:

    >>> ns = SimpleNamespace(roses='red', violets='blue')
    >>> thing = input()
    >>> quality = input()
    >>> setattr(ns, thing, quality)            # current
    >>> ns['sugar'] = 'sweet'                   # proposed

If the PEP 584 __ior__ method were supported, updating a SimpleNamespace would be much cleaner:

      ns |= some_dict

I posted an issue on the tracker: https://bugs.python.org/issue40284 .  There was a suggestion to create a different type for this, but I don't see the point in substantially duplicating everything SimpleNamespace already does just so we can add some supporting dunder methods.   Please add more commentary so we can figure-out the best way to offer this powerful functionality.


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