On 2022-04-03 17:58:09 +0300, Kirill Ratkin via Python-list wrote:
> 02.04.2022 23:44, Marco Sulla пишет:
> > A proposal. Very often dict are used as a deeply nested carrier of
> > data, usually decoded from JSON. Sometimes I needed to get some of
> > this data, something like this:
> >
> > data["users"][0]["address"]["street"]
> >
> > What about something like this instead?
> >
> > data.get_deep("users", 0, "address", "street")
Yup. I need something like this quite frequently, so I wrote a little
utility function (which I copy and paste into lots of code - I probably
should package that up, but a package with a single short function feels
weird).
[...]
> > data.get_deep("users", 0, "address", "street", default="second star")
Yep. Did that, too. Plus pass the final result through a function before
returning it.
I'm not sure whether I considered this when I wrote it, but a function
has the advantage of working with every class which can be indexed. A
method must be implemented on any class (so at least dict and list to be
useful).
> Recently I met same issue. A service I intergated with was documented badly
> and sent ... unpredictable jsons.
>
> And pattern matching helped me in first solution. (later I switched to
> Pydantic models)
>
> For your example I'd make match rule for key path you need. For example:
>
>
> data = {"users": [{"address": {"street": "Baker"}}]}
>
> match data:
> case {"users": [{"address": {"street": street}}]}:
> print(f"street: {street}")
>
> case _:
> print("unsupported message structure")
Neat. But that's 5 lines instead of one. I simple loop around try/except
also takes 5 lines, and the latter can be easily moved into a function,
like this:
def get_nested(coll, path, default=None, cast=None):
for i in path:
try:
coll = coll[i]
except (KeyError, IndexError, TypeError):
return default
if cast:
coll = cast(coll)
return coll
which can then be called in a single line.
> Structural matching gives you warranty you process exactly message you
> expect and explicitly discards messages with another structure.
True, and sometimes useful, I'm sure. Not sure whether it would have
helped me in the cases where I used the utility function above.
hp
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