Passing more than two sys.argv in python
from visa import *
import sys
inst = instrument(sys.argv[1])
inst.write("*rst; status:preset; *cls")
inst.write("voltage:UNIT Vrms")
inst.write("apply:SIN %s %s" % sys.argv[2] % sys.argv[3])

from visa import *
import sys
inst = instrument("USB0::0x164E::0x13EC::TW00008555")
inst.write("*rst; status:preset; *cls")
inst.write("voltage:UNIT Vrms")
inst.write("apply:SIN 1000, 0.5")

inst.write("apply:SIN %s %s" % (sys.argv[2], sys.argv[3]))

inst.write("apply:SIN %s, %s" % (sys.argv[2], sys.argv[3]))

>>> "test %s %s" % ("a", "b")
'test a b'

>>> "test {0} {1}".format("a", "b")
'test a b'

inst.write("apply:SIN {0}, {1}".format(sys.argv[2], sys.argv[3]))