How to access Ramp by python

gistfile1.py

node_name = '/obj/geo1/null1'
ramp_name = 'color'
n = hou.node(node_name)
ramp = n.parm(ramp_name).evalAsRamp()
for i in range(len(ramp.keys())):
    # Position
    # get
    pos = n.parm('%s%dpos' % (ramp_name, i+1)).eval()
    # set
    n.parm('%s%dpos' % (ramp_name, i+1)).set(pos * 0.5)
    # Color
    # get
    r = n.parm('%s%dcr' % (ramp_name, i+1)).eval()
    g = n.parm('%s%dcg' % (ramp_name, i+1)).eval()
    b = n.parm('%s%dcb' % (ramp_name, i+1)).eval()
    # set
    n.parm('%s%dcr' % (ramp_name, i+1)).set(pos)
    n.parm('%s%dcg' % (ramp_name, i+1)).set(pos)
    n.parm('%s%dcb' % (ramp_name, i+1)).set(pos)