Automatically grow the bbox of a Nuke node unioning animation

grow.py

import nuke,os

"""
Will make a Crop node that crops the frame to the union of the animated BBox of the nude currently selected.
For example, if you have a Tracker node that stabilizes an image this function will  grow your bounding box
to include the whole stabilized image
"""
def grow_bbox():
	sel = nuke.selectedNode()
	xmin = 0
	xmax = 0
	ymin = 0
	ymax = 0
	# The trick is that we need to execute() some node every time we go to a next frame, to
	# update the context.
	# not any node can be executed(). Now, for Nuke 6.2+ you can feed the knobs an input context
	# to evaluate the knobs at specific frames BUT bbox is not a knob, it's the node's property.
	# So we create a CurveTool that we can execute() on every frame.
	c = nuke.nodes.CurveTool()
	f = nuke.frame()
	
	# Python ranges are NOT inclusive therefore +1
	for i in range(nuke.root().firstFrame(), nuke.root().lastFrame() + 1):
		nuke.execute(c, i, i) # Workaround to update the tree
		bbox = sel.bbox()
		rx = bbox.x() + bbox.w()
		ry = bbox.y() + bbox.h()
		if xmin > bbox.x():
			xmin = bbox.x()
		if xmax < rx:
			xmax = rx
		if ymin > bbox.y():
			ymin = bbox.y()
		if ymax < ry:
			ymax = ry
	
	nuke.delete(c)
	
	c = nuke.nodes.Crop()
	c["name"].setValue("GrowCrop")
	c["reformat"].setValue(True)
	c["box"].setValue((xmin, ymin, xmax, ymax))
	c.setInput(0, sel)
	
	# Return the frame to it's old position
	nuke.frame(f)

if nuke.GUI:
	toolbar = nuke.menu("Nodes")
	heMenu = toolbar.findItem("Useful")
	ico = os.path.dirname(os.path.abspath(__file__)) + "/grow_bbox.png"
	heMenu.addCommand("Union bbox across frames", command="grow_bbox()",  icon=ico, tooltip = str(grow_bbox.__doc__))