Select subregion of 1st grid based on size of 2nd grid using python script

Dear ParaView users,

I have two grids (big, small) that overlay (top in Figure 1).
I would like to extract a subregion out of the big grid similar as in bottom of Figure 1.
The subregion should match an axis aligned boundary box of the small grid.
I did this approximately using the Clip filter using the GUI.
However, I would like to do this automatically using a Python script based on the max and min point coordinates of the small grid.

I was not able to extract the point coordinates of the small grid in python (sript and shell) to pass them to the Clip filter.
Within a ProgrammableFilter it is easy to access the point coordinates via input.Points[:,0], however, within a ProgrammableFilter I was not able to access a Clip filter.

How do I access point coordinates in a python script or in the python shell?