slugify should take an optional max length

[Jeremy Dunck]

A SlugField has a max_length of 50 by default, but the slugify template filter does not easily truncate.

Perhaps altering to something like this would be helpful:

SLUG_RE = re.compile('\-[^\-]*$')
def slugify_max(text, max_length=50):
        slug = slugify(text)
        last_len = len(slug)
        while len(slug) > max_length:
            slug = SLUG_RE.sub('', slug)

            # avoid infinite loop
            if len(slug) == last_len:
                break
            last_len = len(slug)
        slug = slug[:max_length] #hack off end if unable to nicely crop it.
        return slug

Design decision needed because I'm not sure folks will agree this is needed in core.

[Keryn Knight <keryn@…>]

1. Would we really require an entirely separate filter to handle an 'optional' use case?
2. Can the same functionality not be provided by {{ thing|slugify|slice:"N" }} ?

[Jeremy Dunck]

1) No, I was just using it for illustrative purposes. It'd just be an optional to slugify.
2) Well, I'm trying to preserve word boundaries there, "this is an example headline" -> "this-example-headline" -> "this-example", not "this-example-he" if length were 15.

[Aymeric Augustin]

Indeed, I'm not sure this belongs to core:

• The relation to the max_length of SlugField isn't obvious to me — and if a form field was involved, a human would be better than a computer at shortening its contents while preserving its meaning.
• It's easy to implement your idea as a custom template filter (I hope you've done so).
• I'd prefer to keep slugify simple.

Thanks for the suggestion anyway!

[Andrew Badr]

Here's a more efficient version of slugify_max, if anyone comes looking.

def slugify_max(text, max_length=50):
    slug = slugify(text)
    if len(slug) <= max_length:
        return slug
    trimmed_slug = slug[:max_length].rsplit('-', 1)[0]
    if len(trimmed_slug) <= max_length:
        return trimmed_slug
    # First word is > max_length chars, so we have to break it
    return slug[:max_length]