import maya.cmds
import maya.mel as mel

import maya.cmds
import maya.mel as mel

cmds.currentUnit( time='ntsc' )
fps = mel.eval('currentTimeUnitToFPS')
print fps
# 30.0

cmds.currentUnit( time='250fps' )
fps = mel.eval('currentTimeUnitToFPS')
print fps
# 250.0