Decoding bencoded data with python

From TheoryOrg

I've written this because bencode.py in the BitTorrent source doesn't really handle nested bencoded data found in scrapes and this is on average 5-6 times faster than the perl implementation -- Hackeron

import re
try:
    import psyco # Optional, 2.5x improvement in speed
    psyco.full()
except ImportError:
    pass

decimal_match = re.compile('\d')

def bdecode(data):
    '''Main function to decode bencoded data'''
    chunks = list(data)
    chunks.reverse()
    root = _dechunk(chunks)
    return root

def _dechunk(chunks):
    item = chunks.pop()

    if (item == 'd'): 
        item = chunks.pop()
        hash = {}
        while (item != 'e'):
            chunks.append(item)
            key = _dechunk(chunks)
            hash[key] = _dechunk(chunks)
            item = chunks.pop()
        return hash
    elif (item == 'l'):
        item = chunks.pop()
        list = []
        while (item != 'e'):
            chunks.append(item)
            list.append(_dechunk(chunks))
            item = chunks.pop()
        return list
    elif (item == 'i'):
        item = chunks.pop()
        num = ''
        while (item != 'e'):
            num  += item
            item = chunks.pop()
        return int(num)
    elif (decimal_match.findall(item)):
        num = ''
        while decimal_match.findall(item):
            num += item
            item = chunks.pop()
        line = ''
        for i in range(1, int(num) + 1):
            line += chunks.pop()
        return line
    raise "Invalid input!"

Note: this implementation turns out to be ca. twice as slow as the original Python implementation from Brahm Cohen, if psyco is not available. Anybody interested in using those encoding and decoding methods can do so with a standalone package from the Cheese Shop.