ENH: Add a data_preload step in pandas backend #1142
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@wesm can you review this when you get a chance? |
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Aug 28, 2017
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@wesm thanks! |
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This PR adds a
data_preloadstep to the execution pipeline for the Pandasbackend.
The motivation for this is to allow clients to perform operations on
(Node, ConcreteData)pairs (including ascopeargument) before the executionfor a particular operation starts.
Custom data source execution is the main use case here.
As a motivating example, consider a custom data source object that can be
turned into a DataFrame.
We want to be able to operate on our custom data source, but we don't want to
redefine every operation for this data source, or it doesn't make sense to
define operations on this custom object directly.
data_preloadgives the ability to call a function on data pieces that are in scope before any execution happens. In the example above,data_preloadwould turn theConcreteDataobject into apandas.DataFrame.The default behavior is no-op.
This also sets the stage for multi-client execution. More on that to come.