python: print nested datatypes.

[Hoeze]

I really like the printSchema() function in PySpark as it massively simplifies working with (large) tables: Having this function in polars as well would aid its usage comfort :)

[ritchie46]

Something like this?:

from pprint import pprint

pprint(df.schema)

{'dropoff_datetime': <class 'polars.datatypes.Utf8'>,
 'dropoff_latitude': <class 'polars.datatypes.Float64'>,
 'dropoff_longitude': <class 'polars.datatypes.Float64'>,
 'fare_amount': <class 'polars.datatypes.Float64'>,
 'mta_tax': <class 'polars.datatypes.Float64'>,
 'passenger_count': <class 'polars.datatypes.Int64'>,
 'payment_type': <class 'polars.datatypes.Utf8'>,
 'pickup_datetime': <class 'polars.datatypes.Utf8'>,
 'pickup_latitude': <class 'polars.datatypes.Float64'>,
 'pickup_longitude': <class 'polars.datatypes.Float64'>,
 'rate_code': <class 'polars.datatypes.Int64'>,
 'store_and_fwd_flag': <class 'polars.datatypes.Int64'>,
 'surcharge': <class 'polars.datatypes.Float64'>,
 'tip_amount': <class 'polars.datatypes.Float64'>,
 'tolls_amount': <class 'polars.datatypes.Float64'>,
 'total_amount': <class 'polars.datatypes.Float64'>,
 'trip_distance': <class 'polars.datatypes.Float64'>,
 'vendor_id': <class 'polars.datatypes.Utf8'>}

[Hoeze]

Yes, but the difference is that this one does not show nested structures:

[ritchie46]

Right, so we should improve the print of our nested structures!

[ghuls]

Right, so we should improve the print of our nested structures!

The doctest that I fixed recently had the name of the fields for structs in the old output. So it seems that at least for structs it was once implemented.

[phillyphil91]

I will take a look at this and see how to implement the nested dtypes on the rust side as suggested.

Would this be a good starting point for the dtypes in general: ?:

https://github.com/pola-rs/polars/blob/9344555b3133626b56a5bf6e207d347f9badbd8e/polars/polars-core/src/datatypes/mod.rs

[mslapek]

I think this issue can be closed.

When we run df.schema on recent polars, we get a description of the struct fields:

{'name': Utf8, 'car': Struct([Field('color', Utf8), Field('year', Int64)])}

(It was noticed by @phillyphil91 in https://github.com/pola-rs/polars/pull/4213#issuecomment-1367542011)