Date transformers casting dtypes if passed in as an input

[Decima2014]

We have had some issues in the past with some tubular date transformers requiring conflicting specific dtypes to be accepted by the transformer, ie: datetime.object, datetime.date, datetime[n64].

The ExtractTimeInfo and DateDifferenceTransformer for example requiring different dtypes

I believe having an option to automatically cast the column to the required dtype as opposed to directly failing would be preferable

[Decima2014]

You sometimes dont want your datetime columns to be casted to a new type even if that type is what the transformer requires, so your dates transformers could use a temporary copy of the column for the transformation

[TommyMatthews]

Will look at this this sprint

[TommyMatthews]

DateDiffLeapYearTransformer also raises an error incorrectly when passed a datetime object

[TommyMatthews]

I've had a look at this and it looks like the conflicting dtypes can be quickly fixed by making a BaseDateTimeTransformer and adding a standardised datetime input check that all of the transformers use. This should make it much easier to put columns in the right format beforehand with a ToDateTimeTransformer.

With regards to casting, I think this would be a lot more faff to do, create scope for a lot more hidden errors and make a lot of testing overhead, especially given that the copy datetime columns can be created using a to datetime transformer one step before in the pipeline.

@davidhopkinson26 @Decima2014

[TommyMatthews]

I've characterised the problem slightly more. Considering the two main datetime datatypes, datetime.date and datetime.datetime:

• DateTimeInfoExtractor: only works on datetime.datetime due to how it's written - needs the .dt accessor only available to datetime.datetime objects. I think this unavoidably needs temporary casting inside transform for full consistency across dates.py

• DateDifferenceTransformer: works with either datetime.datetime or datetime.time, but can't handle the combination of the two types across the two columns. Think this should be a quick fix.

• DateDifferenceLeapYearTransformer: no issues once I fix the input checks.