メモリの問題を発生させずに、Python 2.7 で巨大な CSV ファイルを効率的に処理するにはどうすればよいでしょうか?

import csv

def getstuff(filename, criterion):
    with open(filename, "rb") as csvfile:
        datareader = csv.reader(csvfile)
        yield next(datareader)  # yield header row

        count = 0
        for row in datareader:
            if row[3] == criterion:
                yield row
                count += 1
            elif count:  # stop processing when a consecutive series of non-matching rows is encountered
                return

from itertools import dropwhile, takewhile

def getstuff(filename, criterion):
    with open(filename, "rb") as csvfile:
        datareader = csv.reader(csvfile)
        yield next(datareader)  # yield header row

        yield from takewhile(  # yield matching rows
            lambda r: r[3] == criterion,
            dropwhile(  # skip non-matching rows
                lambda r: r[3] != criterion, datareader))
        return

def getdata(filename, criteria):
    for criterion in criteria:
        for row in getstuff(filename, criterion):
            yield row