scene = cur_desktop.paneTabOfType(hou.paneTabType.SceneViewer)
flip_options = scene.flipbookSettings().stash()
flip_options.frameRange( (frame, frame) )
flip_options.output(filename)
scene.flipbook(scene.curViewport(), flip_options)

import traceback
from os.path import dirname,basename,splitext

def getSceneViewer():
    """
    return an instance of a visible viewport. 
    There may be many, some could be closed, any visible are current
    """
    panetabs = hou.ui.paneTabs()
    panetabs = [x for x in panetabs if x.type() == hou.paneTabType.SceneViewer]
    panetabs = sorted(panetabs, key=lambda x: x.isCurrentTab())
    if panetabs:
        return panetabs[-1]
    else:
        print("No SceneViewers detected.")
        return None
    
   
def viewwrite():
    """
    Get the current sceneviewer (may be more than one or hidden)
    and screengrab the perspective viewport to a file in the 
    publish location to be picked up with the publish. 
    
    Note that .png output will render pooly, so use .jpg   
    """
    try:
        node = hou.node(".")
        path = node.parm("outputpath").eval()       
        file,ext = splitext(basename(path))
        filename = f'{dirname(path)}/{file}.jpg'
        frame = hou.frame()
    
        desktop = hou.ui.curDesktop()
        sceneview = getSceneViewer()
        viewport = sceneview.curViewport()
    
        # this will open an mplay window to show the result
        fbs = sceneview.flipbookSettings().stash()
        fbs.frameRange( (frame, frame) )
        fbs.output(filename)
        fbs.outputToMPlay(False)
        sceneview.flipbook(viewport, fbs)
            
    except Exception as e:
        print(f'ERROR: Failed to Capture Viewport\n{traceback.format_exc(2)}')