issues: 1217425815

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
1217425815 I_kwDOAMm_X85IkHGX 6524 NumPy `__array_ufunc__` does not work with typing 61316 open 0     6 2022-04-27T14:16:00Z 2022-06-05T19:54:47Z   NONE      

What is your issue?

When using NumPy functions which have been patched to work with xarray objects using __array_ufunc__, typing tools like MyPy do not correctly calculate the return value.

For example, the function np.exp has been adapted by xarray to return a DataArray if it is passed a DataArray, so that code like the following will work:

```python import xarray as xr import numpy as np

da = xr.DataArray([1, 2, 3, 4]) blah = np.exp(da).rename("blah") ```

This code creates an xr.DataArray, uses numpy to calculate the exp of its values and then, since it is returned as a xr.DataArray it can call xarray methods like rename on it.

However, running MyPy on this code gives the error:

error: "ndarray[Any, dtype[Any]]" has no attribute "rename"

This is because there is typing information from NumPy which claims that np.exp returns ndarray[Any, dtype[Any]].

Now, I'm unsure whether this is a bug in xarray not providing the typing information to the __array_ufunc__ code, a bug in NumPy for not having the flexibility to type these overrides or in MyPy for now allowing for overrides like this to happen but I wanted to star with the place where the observed error occurs.

 
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     13221727 issue

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