external merge sort

import time
import sys
import os
from heapq import heappop, heappush
from itertools import islice
from tempfile import gettempdir

LINES_BUFFER = 2000  # 1MB / 502 bytes
KB_64 = 64 * 1024


def merge(chunks):
    key = lambda x: x
    values = []
    for index, chunk in enumerate(chunks):
        try:
            iterator = iter(chunk)
            value = iterator.next()
        except StopIteration:
            try:
                chunk.close()
                os.remove(chunk.name)
                chunks.remove(chunk)
            except:
                pass
        else:
            heappush(values, (key(value), index, value, iterator, chunk))

    while values:
        k, index, value, iterator, chunk = heappop(values)
        yield value
        try:
            value = iterator.next()
        except StopIteration:
            try:
                chunk.close()
                os.remove(chunk.name)
                chunks.remove(chunk)
            except:
                pass
        else:
            heappush(values, (key(value), index, value, iterator, chunk))


def external_sort(input_file, output_file):
    temp_dir = gettempdir()
    input_file = file(input_file, 'rb', KB_64)
    try:
        input_iterator = iter(input_file)
        chunks = []
        output_chunk = None
        try:
            while True:
                current_chunk = list(islice(input_iterator, LINES_BUFFER))
                if current_chunk:
                    current_chunk.sort()
                    output_chunk = file(os.path.join(temp_dir, '%06i' % len(chunks)), 'w+b', KB_64)
                    output_chunk.writelines(current_chunk)
                    output_chunk.flush()
                    output_chunk.seek(0)
                    chunks.append(output_chunk)
                else:
                    break
        except:
            for chunk in chunks:
                try:
                    chunk.close()
                    os.remove(chunk.name)
                except:
                    pass
            if output_chunk not in chunks:
                try:
                    output_chunk.close()
                    os.remove(output_chunk.name)
                except:
                    pass
            return
    finally:
        input_file.close()

    output_file = file(output_file, 'wb', KB_64)
    try:
        output_file.writelines(merge(chunks))
    finally:
        for chunk in chunks:
            try:
                chunk.close()
                os.remove(chunk.name)
            except:
                pass
        output_file.close()


if __name__ == '__main__':
    t = time.time()
    if len(sys.argv) < 2:
       print("Input [output] file(s) please....")
    else:
       external_sort(sys.argv[1], sys.argv[2] if len(sys.argv) > 2 else "%s.out" % sys.argv[1])
       print("Sorted in %f sec." % (time.time() - t))