Re: [Python-markdown-discuss] second Markdown() instance clobbers the first?

[Yuri T. <qar...@gm...>]

Your expectations are correct, the behavior is wrong, so it's a bug.

The reason for this is that it looks like different instances of
Markdown share the same instances of patterns.  For instance, we have:

REFERENCE_PREPROCESSOR = ReferencePreprocessor()

So, REFERENCE_PREPROCESSOR is a module-level variable and the instance
is shared.  This gives later instances an opportunity to change it
during initialization.

I think we have two options: we can either make all the patterns
stateless, and give them an instance of Markdown() if they want to
look up config parameters.  Or we could give each instance of Markdown
it's own set of patterns.  I am leaning on the second solution, but
note the downside: the we are relying on those variables in the
extensions, so this would break many of the extensions.  If we'll be
doing this, we might as well make the effort now to add a treap for
ordering the preprocessor, as Ben Wilson suggested last year.

Then, we would have something like:

    self.preprocessors = Treap('header', HeaderPreprocessor())
    self.preprocessors.insert_after('header', 'line', LinePreprocessor())
    self.preprocessors.insert_after('line', 'reference',
ReferencePreprocessor())

In the footnote extension we can then have:

    md.preprocessors.insert_before('reference', 'footnote',
FootnotePreprocessor())

What do you guys think?

- yuri

On Thu, Sep 25, 2008 at 11:39 PM, Eric Abrahamsen <er...@ab...> wrote:
> I'm using Markdown with Django, not as a template filter but by
> running database text through markdown as it is saved, so that the
> markdown text is saved into one field, and HTML converted text is
> saved into another field. I want different behavior for different
> models, so I instantiate two Markdown objects, one for filtering blog
> entry text (safe_mode is off) and one for filtering comment text
> (safe_mode is set to 'remove').
>
> Both are instantiated at the top of a single models.py module, like
> this:
>
> safe_md = Markdown()
> remove_md = Markdown(safe_mode='remove')
>
> What I've found is that the second instance seems to override the
> first. Blog text run through safe_md.convert() has its HTML removed,
> as though its safe_mode were set to 'remove'. I "fixed" the problem by
> commenting out the second instance, and later I moved it inside a
> function where it's hidden.
>
> This isn't at all how I expected this to work, and I wonder if it's a
> bug with Markdown or with my expectations. I thought it might have had
> to do with Django, perhaps threading or something, but it behaves the
> same way in the Python interpreter. Can someone explain what's going
> on here?
>
> TIA,
>
> Eric
>
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