A gamspy.Number() object is needed for assigning records to a symbol conditionally. For example:

import gamspy as gp
m = gp.Container()
k = gp.Set(m, "k", records=["1964-i","1964-ii","1964-iii","1964-iv"])
ki = gp.Set(m, name="ki", domain=[k], description="initial period")
ki[k] = gp.Number(1).where[gp.Ord(k) == 1]

The code snippet above would assign only 1964-i to ki since only the order of 1964-i is equal to 1.