[Python]: Expose Dataframe.schema() to Python binding

[mmuru]

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In Python, trying to get schema from Dataframe but it is not available in Python binding. Ideally, we should expose all the dataframe methods in Python binding.

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In Python, I should able to get schema from dataframe.

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[mmuru]

@houqp: I reviewed the current implementation schema() in dataframe_impl.rs and it returns &DFSchema. In Python, how do I return it? Please, review this request and provide your feedback. Thanks.

[houqp]

I haven't put a lot of thought into this, so take it with a grain of salt ;)

I think one possible solution would be creating a new wrapper struct that wraps the DFSchema type within the python crate, then annotate it with pyclass (https://pyo3.rs/master/class.html#defining-a-new-class) so the wrapper type can be returned directly to python. You won't be able to return a reference to python, so you need to clone the &DFSchema reference and store it inside the wrapper struct.

[drauschenbach]

This appears to be resolved. In datafusion-python, I can call df.schema(). In any case, this concern has moved to the datafusion-python git repo.

[andygrove]

Closing this. Thanks @drauschenbach.