>>> import arcpy
... fc = "Flight_Demo5_LineToPoints"
... n = 1
... with arcpy.da.UpdateCursor(fc, "alternate") as cursor:
...     for row in cursor:
...         if n == 1:
...             row[0] = 1
...             n = n - 1
...         else:
...             row[0] = 0
...             n = n + 1
...         cursor.updateRow(row)