Comment by tzot

11 hours ago

Well, we can use memoryview for the dict generation avoiding creation of string objects until the time for the output:

    import re, operator
    def count_words(filename):
        with open(filename, 'rb') as fp:
            data= memoryview(fp.read())
        word_counts= {}
        for match in re.finditer(br'\S+', data):
            word= data[match.start(): match.end()]
            try:
                word_counts[word]+= 1
            except KeyError:
                word_counts[word]= 1
        word_counts= sorted(word_counts.items(), key=operator.itemgetter(1), reverse=True)
        for word, count in word_counts:
            print(word.tobytes().decode(), count)

We could also use `mmap.mmap`.

7 comments

tzot

Reply
akx  9 hours ago

This doesn't do the same thing though, since it's not Unicode aware.

    >>> 'x\u2009   a'.split()
    ['x', 'a']
    # incorrect; in bytes mode, `\S` doesn't know about unicode whitespace
    >>> list(re.finditer(br'\S+', 'x\u2009   a'.encode()))
    [<re.Match object; span=(0, 4), match=b'x\xe2\x80\x89'>, <re.Match object; span=(7, 8), match=b'a'>]
    # correct, in unicode mode
    >>> list(re.finditer(r'\S+', 'x\u2009   a'))
    [<re.Match object; span=(0, 1), match='x'>, <re.Match object; span=(5, 6), match='a'>]

  • contravariant  9 hours ago

    There's bound to be a way to turn a stream of bytes into a stream of unicode code points (at least I think that's what python is doing for strings). Though I'm explicitly not volunteering to write the code for it.

    • est  6 hours ago 

          import mmap, codecs

    from collections import Counter

    def word_count(filepath):

        freq = Counter()
    
        decode = codecs.getincrementaldecoder('utf-8')().decode
    
        with open(filepath, 'rb') as f, mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ) as mm:
        
                for chunk in iter(lambda: mm.read(65536), b''):
            
                        freq.update(decode(chunk).split())
            
                    freq.update(decode(b'', final=True).split())
        
                return freq

    • zahlman  6 hours ago

      Sure, but making one string from the file contents is surely much better than having a separate string per word in the original data.

      ... Ah, but I suppose the existing code hasn't avoided that anyway. (It's also creating regex match objects, but those get disposed each time through the loop.) I don't know that there's really a way around that. Given the file is barely a KB, I rather doubt that the illustrated techniques are going to move the needle.

      In fact, it looks as though the entire data structure (whether a dict, Counter etc.) should a relatively small part of the total reported memory usage. The rest seems to be internal Python stuff.

contravariant  9 hours ago

For reasons I never quite understood python has a collections.Counter for the purpose of counting things. It's a bit cleaner.