getUParam

from maya import cmds , OpenMaya

def getUParam( pnt = [], crv = None):

    point = OpenMaya.MPoint(pnt[0],pnt[1],pnt[2])
    curveFn = OpenMaya.MFnNurbsCurve(getDagPath(crv))
    paramUtill=OpenMaya.MScriptUtil()
    paramPtr=paramUtill.asDoublePtr()
    isOnCurve = curveFn.isPointOnCurve(point)
    if isOnCurve == True:
        
        curveFn.getParamAtPoint(point , paramPtr,0.001,OpenMaya.MSpace.kObject )
    else :
        point = curveFn.closestPoint(point,paramPtr,0.001,OpenMaya.MSpace.kObject)
        curveFn.getParamAtPoint(point , paramPtr,0.001,OpenMaya.MSpace.kObject )
    
    param = paramUtill.getDouble(paramPtr)  
    return param

def getDagPath( objectName):
    
    if isinstance(objectName, list)==True:
        oNodeList=[]
        for o in objectName:
            selectionList = OpenMaya.MSelectionList()
            selectionList.add(o)
            oNode = OpenMaya.MDagPath()
            selectionList.getDagPath(0, oNode)
            oNodeList.append(oNode)
        return oNodeList
    else:
        selectionList = OpenMaya.MSelectionList()
        selectionList.add(objectName)
        oNode = OpenMaya.MDagPath()
        selectionList.getDagPath(0, oNode)
        return oNode