Question

I found some this promising code on activestate.com to sort huge files. I’m trying to run it on the default Python 2.6.5 interpreter on Ubuntu 10.04. When I try running it on a small test file, I get the error trace below. I asked for help on activestate.com, but this thread has been silent for over 18 months. Is there anyone here who sees an obvious solution?

Thanks.

## {{{ http://code.activestate.com/recipes/576755/ (r3)
# based on Recipe 466302: Sorting big files the Python 2.4 way
# by Nicolas Lehuen

import os
from tempfile import gettempdir
from itertools import islice, cycle
from collections import namedtuple
import heapq

Keyed = namedtuple("Keyed", ["key", "obj"])

def merge(key=None, *iterables):
    # based on code posted by Scott David Daniels in c.l.p.
    # http://groups.google.com/group/comp.lang.python/msg/484f01f1ea3c832d

    if key is None:
        keyed_iterables = iterables
    else:
        keyed_iterables = [(Keyed(key(obj), obj) for obj in iterable)
                            for iterable in iterables]

    for element in heapq.merge(*keyed_iterables):
        yield element.obj


def batch_sort(input, output, key=None, buffer_size=32000, tempdirs=None):
    if tempdirs is None:
        tempdirs = []
    if not tempdirs:
        tempdirs.append(gettempdir())

    chunks = []
    try:
        with open(input,'rb',64*1024) as input_file:
            input_iterator = iter(input_file)
            for tempdir in cycle(tempdirs):
                current_chunk = list(islice(input_iterator,buffer_size))
                if not current_chunk:
                    break
                current_chunk.sort(key=key)
                output_chunk = open(os.path.join(tempdir,'%06i'%len(chunks)),'w+b',64*1024)
                chunks.append(output_chunk)
                output_chunk.writelines(current_chunk)
                output_chunk.flush()
                output_chunk.seek(0)
        with open(output,'wb',64*1024) as output_file:
            output_file.writelines(merge(key, *chunks))
    finally:
        for chunk in chunks:
            try:
                chunk.close()
                os.remove(chunk.name)
            except Exception:
                pass

Error trace:

Traceback (most recent call last):
  File "./batch_sort.py", line 108, in <module>
    batch_sort(args[0],args[1],options.key,options.buffer_size,options.tempdirs)
  File "./batch_sort.py", line 54, in batch_sort
    output_file.writelines(merge(key, *chunks))
  File "./batch_sort.py", line 30, in merge
    yield element.obj
AttributeError: 'str' object has no attribute 'obj'

Answer 1

The code for merge is incorrect.
If you don’t provide a key, each element is a string instead of a keyed tuple.

Try this instead:

def merge(key=None, *iterables):
    # based on code posted by Scott David Daniels in c.l.p.
    # http://groups.google.com/group/comp.lang.python/msg/484f01f1ea3c832d

    if key is None:
        for element in heapq.merge(*iterables):
            yield element
    else:
        keyed_iterables = [(Keyed(key(obj), obj) for obj in iterable)
                        for iterable in iterables]
        for element in heapq.merge(*keyed_iterables):
            yield element.obj