>>> cities = open('c:\cities.raw')
>>> out = open('cities2.raw', 'wb')
>>> i = 0
>>> 21162 / 4
5290
>>> chunk = cities.read(5290)
>>> while chunk:
	if i % 4 is not 2:
		out.write(chunk)
	i += 1
	chunk = cities.read(5290)


>>>