Add a safe_get_config

[BryceStevenWilley]

We've added a lot of chained code that gets things from the config, i.e.:

x = get_config("assembly line", {}).get("interview list")

This is fine, but there's an issue if people have something wrong in their config file, like this error recently in teams:

  File "/usr/share/docassemble/local3.10/lib/python3.10/site-packages/docassemble/AssemblyLine/sessions.py", line 1303, in config_with_language_fallback
    if interview_list_config.get(config_key):
AttributeError: 'NoneType' object has no attribute 'get'

Which has to be caused by a call to get_config("assembly line", {}) being present (so the empty dict isn't returned), but still returning null.

My question is if we want a safer version, like safe_get_config that internally would be something like this:

def safe_get_config(config_key, *further_keys):
    obj = get_config(config_key) or {}
    for config_key in further_keys:
        obj = obj.get(config_key) or {}
    return obj

Making sure that we would never have a no attribute 'get' error in production, no matter what the config looks like. Cons are that it might be harder to determine a misconfigured server, but IMO there's enough issues with YAML and spelling and stuff that hiding None key-values in dictionaries shouldn't make the problem worse.

[nonprofittechy]

This could help simplify a common pattern. I'm open to it. I did look into whether there's a good existing tool or pattern for this, like xpath for XML. There is dpath, but it's a pretty heavy dependency and we're just using one possible option of it, so a new function seems fine.

[BryceStevenWilley]

Dumping my progress so far on this: code is in https://github.com/SuffolkLITLab/docassemble-ALToolbox/tree/safe_config.

I had intended for it to be used as safe_get_config("assembly line", "interview list", "special key") or "default", but that prevents people from ever setting things as blank strings, and it would always get overriden by "default". So a slight change in the definition (looks fairly close to a version I wrote in EFSPIntegration):

def safe_get_config(config_keys: List[str], default: Any) -> Any:

Internally, we can return the default whenever to_return is None. I haven't seen null explicitly set in a config on MassAccess or MPLP, so I think that's fine.

I also slowed down on this because we rarely have configs that are nested beyond 2 dictionaries in the config, so adding this function doesn't avoid any really gnarly code.