Repository: opencv
Issue: Python GpuMat not subscriptable
Labels: feature,category: python bindings,category: gpu/cuda (contrib)

##### System information (version)
- OpenCV => 4.6.0
- Operating System / Platform => Windows 10, 64 Bit
- Compiler => Visual Studio 2017

##### Detailed description

`GpuMat` in the Python bindings is missing support for `__getitem__`

From my understanding the `GpuMat` class is supposed to behave mostly the same as the `Mat` class.
`__getitem__` works on the `Mat` class but not on the `GpuMat` class.

I am using OpenCV with Python. I think this is the correct place to report this.
I would try and debug this issue myself but I don't know where to find the python bindings or how they are generated.

##### Steps to reproduce

I would expect getitem to work on the GpuMat class.
```py
import cv2
im = cv2.cuda.GpuMat(10, 10, cv2.CV_8UC1)
im_slice = im[:2, :2]
```
`TypeError: 'cv2.cuda.GpuMat' object is not subscriptable`

The behaviour works correctly on the Mat class
```py
import numpy
a = numpy.arange(16).reshape(4,4)
im = cv2.Mat(a)
im_slice = im[:2, :2]
```

It could just be that I am misunderstanding the documentation. There is very little Python documentation in this part of the code.

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