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Clarify if interchange dataframes should also have __dataframe__() #80
Description
I couldn't work out if the interchange dataframe (i.e. the dataframe returned from __dataframe__()) should also have a __dataframe__() method, e.g.
>>> import pandas as pd
>>> df = pd.DataFrame() # i.e. the top-level dataframe
>>> interchange_df1 = df.__dataframe__()
>>> interchange_df2 = interchange_df1.__dataframe__()With the upstream of current adopters, we have a split on whether the interchange dataframe has this method.
| Library | Top-level | Interchange |
|---|---|---|
| pandas | ✔️ | ✔️ |
| vaex | ✔️ | ❌ |
| modin | ✔️ | ✔️ |
| cuDF | ✔️ | ❌ |
I had assumed that interchange dataframes should have __dataframe__() by virtue of it being a method in the DataFrame API object. I think it makes sense, as then from_dataframe()-like functions only need to check for __dataframe__() to support interchanging both top-level and interchange dataframes of different libraries.
If there is explicit specification somewhere in this regard then please give me a pointer! In any case, it might be worth clarifying in the __dataframe__() docstring where this method should be residing.
Activity
rgommers commentedon Jul 14, 2022
I'm fairly sure we discussed this once or twice, and that the answer is yes but that there is an inconsistency between spec and implementations. Here is what the spec says currently:
dataframe-api/protocol/dataframe_protocol.py
Lines 307 to 310 in 4f7c1e0
And IIRC the implementations just return
self. My recollection is that we agreed to make all the implementations consistent, and then update the spec. @vnlitvinov please correct me if I'm wrong here.rgommers commentedon Jul 14, 2022
The relevant spec change to return
self(or a'DataFrame'instance in the type annotation) is gh-74, which is about to be merged.Add a `__dataframe__` method to `_VaexDataFrame`
Add a `__dataframe__` method to `_VaexDataFrame`
rgommers commentedon Sep 13, 2022
Pandas: https://github.com/pandas-dev/pandas/blob/7214f85/pandas/core/interchange/dataframe.py#L38-L41
Modin:
Vaex: I just opened vaexio/vaex#2205
cuDF: I just opened NVIDIA/cudf#11692
Add a `__dataframe__` method to `_VaexDataFrame`
Add a `__dataframe__` method to the protocol dataframe object
Add a `__dataframe__` method to the protocol dataframe object (#11692)
Add a `__dataframe__` method to `_VaexDataFrame`
Add a `__dataframe__` method to `_VaexDataFrame` (#2205)