Hi @dudy_karl ,
You declare tensors1 and tensors2 but you reference  tensor1 and tensor2 (with no s) when creating tensors_list. Otherwise what you wrote should work, as such:
def crop_tensors_list(tensors_list):
    for current_tensor in tensors_list:
        current_tensor = current_tensor[:,0:50,0:50]
return tensors_list


tensors1 = torch.randn(4,3,100,100)
tensors2 = torch.randn(4,1,100,100)
tensors_list = [tensors1,tensors2]
tensors_list = crop_tensors_list(tensors_list)