QST: Why is `FutureWarning: Index.__and__ operating as a set operation is deprecated`? 
- [ ] I have searched the [[pandas] tag](https://stackoverflow.com/questions/tagged/pandas) on StackOverflow for similar questions.

- [ ] I have asked my usage related question on [StackOverflow](https://stackoverflow.com).

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#### Question about pandas

I noticed that set comprehension of pandas index are being deprecated.  These are extremely useful.  I was wondering what the rationale for this change is amongst the developers? 

This functionality is extremely useful:
```python
X_A = # Some dataframe (n,m)
X_B = # Some other dataframe (n,q)
X_C = X_A.loc[X_A.columns & X_B.columns]

features = X_A.columns | X_B.columns | X_C.columns

```
