fix(python): allow map_dict on categorical dtype

[coinflip112]

See #7077

[ritchie46]

Thanks! Can you undraft? It should be good to go.

[coinflip112]

Done :)

[cmdlineluser]

Not sure if this is the correct place to comment - but I think if you set the dtype on the 2nd series too it will fix #7140

[coinflip112]

Not sure if this is the correct place to comment - but I think if you set the dtype on the 2nd series too it will fix #7140

The issue is that I'm not sure to what I would be setting the dtype. It can't be the same dtype as the keys of the dictionary.
We would need to infer the type of the values of the mapping dictionary (and this is basically done by polars when the series is created). Maybe we could add an argument which would govern the output type 🤷 Not a fan of the idea though.

[ghuls]

Maybe replace with: input_dtype = df.dtypes[0]

[coinflip112]

Fixed in #7217. I guess I didn't fully realize that we always operate on the first field in the struct 😓

[cmdlineluser]

My bad, I was only thinking in terms of strings/categoricals for some reason - missing the fact that one could be returning a different type from the dict.

I thought the input_dtype could be used if the result was all nulls.