Useful for when you want to set Maya SDK values to work beyond their keyed amount.

bm_setInfinite.py

import maya.cmds as cmds


def setInfinite():
    # get active attr in graph editor
    activeAttr = cmds.animCurveEditor("graphEditor1GraphEd",q=1,cs=1)
    if activeAttr:
        for spline in activeAttr:
            objName = spline[0:spline.index("_")]
            attr = spline[spline.index("_")+1:]
            keyAmt = cmds.keyframe(objName + "." + attr, q=1, keyframeCount = 1)
            # set first and last key to Clamped in and out tangents
            cmds.selectKey(spline,f=(0,0))
            cmds.keyTangent(itt="clamped",ott="clamped")
            cmds.selectKey(spline,f=(keyAmt-1,keyAmt-1))
            cmds.keyTangent(itt="clamped",ott="clamped")
            
            cmds.setInfinity(objName + "." + attr,pri="linear")
            cmds.setInfinity(objName + "." + attr,poi="linear")
    
setInfinite()