import maya.cmds as mc

object = mc.ls(selection =True)[0]
keys = mc.keyframe(object, query =True)

i = 0
while i < len(keys):
	mc.selectKey(object, k =True, time = (keys[i], keys[i]), add =True)
	i = i+2
print "Selected " + str(len(keys[::2])) + " keys: ", str(keys[::2])