Here's some v10.1+ code that calculates an "aspect ratio" in regards to a poly or line FC's hull rectangle (not the same as extent rectangle BTW)... The variables "distance1" and "distance2" are length and width (depending on which one is the longer distance):arcpy.AddField_management(indxTileSinglePartFC, "ASP_RATIO", "DOUBLE")
updateRows = arcpy.da.UpdateCursor(indxTileSinglePartFC, ["SHAPE@","ASP_RATIO"])
for updateRow in updateRows:
    shapeObj = updateRow[0]
    x1,y1,x2,y2,x3,y3,x4,y4 = [float(coord) for coord in shapeObj.hullRectangle.split(" ")]
    distance1 = math.sqrt((x1 - x2)**2 + (y1 - y2)**2)
    distance2 = math.sqrt((x2 - x3)**2 + (y2 - y3)**2)
    if distance1 <= distance2:
        updateRow[1] = distance2 / distance1
    else:
        updateRow[1] = distance1 / distance2
    updateRows.updateRow(updateRow)
del updateRow, updateRows