Type hints: Finish type hints and mark package as typed

[binste]

This will close #2951 🥳

• Build wheel file and test it on a larger Altair code base

[mattijn]

Thanks @binste! Can you briefly explain how these new public types can be used from outside Altair? Would it be possible to import certain types from Altair and do some checks without defining a Chart object?

[binste]

Sure! For example, if you have a function which creates a chart object based on some inputs, it would be great to make sure to test that the passed in data is something that Altair can deal with:

import pandas as pd
import altair as alt


def make_line_chart(data: alt.ChartDataType, x: str, y: str) -> alt.Chart:
    # Imagine that this function creates a more complicated chart spec
    return alt.Chart(data).mark_line().encode(x=x, y=y)


make_line_chart(data=pd.DataFrame(), x="a", y="b")  # This passes
make_line_chart(
    data=2, x="a", y="b"
)  # error: Argument "data" to "make_line_chart" has incompatible type "int"; expected "dict[Any, Any] | DataFrame | _SupportsGeoInterface | _DataFrameLike | Data | str | Generator | UndefinedType"  [arg-type]

For most users, these types/type aliases are probably irrelevant but if you build an application or framework which wants to tightly integrate with Altair, I think they can come in handy.

[mattijn]

Thanks! Shall we make _SupportsGeoInterface and _DataFrameLike public too? Seems useful.

[jonmmease]

Thanks! Shall we make _SupportsGeoInterface and _DataFrameLike public too? Seems useful.

I agree. I think _DataFrameLike should be public since it's the return type of chart.transformed_data(). We expose _SupportsGeoInterface as part of the Union defining the public DataType type, so I think it should be public as well.

[binste]

Fully agree, thanks for catching that.

[mattijn]

Nice! One more question, what is the difference between ChartDataType and DataType?

[mattijn]

I see already:

DataType = Union[dict, pd.DataFrame, SupportsGeoInterface, DataFrameLike]

ChartDataType = Union[DataType, core.Data, str, core.Generator, UndefinedType]

DataType is a subset of ChartDataType

[mattijn]

Congrats @binste! A lot of hard work! Thanks. Let's start testing this within real use cases in the coming period.

[binste]

Thanks! Yeah it was a longer journey but also very educational for me and I hope it's of use. I already tested it on a medium-sized web application which uses many Altair charts and it allowed me to discover some edge cases in the application code which could have led to bugs :)