[Python-markdown-discuss] Bug 1763338 and Max Recursion

[Waylan L. <wa...@gm...>]

Some time ago I looked at bug 176338 [1] and lowered its priority
significantly as the sample input was a far cry from markdown syntax.
I recognized the need for a more graceful way to deal with the issue,
but given the formatting of the text, it didn't seem all that
important.

Thing is, now I realize that the sample text attached to that ticket
was skewing the issue. The bad syntax was just escalating the problem.
The fact is, the current way `_process_section` works (it recursively
calls itself on each block of remaining text), we can easily reach max
recursion with perfectly good syntax.

Therefore, I created a document the following way:

    import sys
    t = ""
    for i in range(sys.getrecursionlimit()):
        t += "Paragraph %d.\n\n" % i

That's 1000 paragraphs one line each - as simple of markdown syntax as
one could have. Even so:

    html = markdown.markdown(t)
    ...
    RuntimeError: maximum recursion depth exceeded

I played with a few different numbers and 985 was the magic number.
The maximum paragraphs a markdown document can have is 984. That's
assuming no lists, blockquotes or anything else that necessarily goes
deeper into recursion.

While replacing recursion with a loop is probably easier said than
done, do we care? In other words, are we ok limiting the possible
length of documents we can process - with that limit becoming shorter
the more complex the syntax used?

If so, I'll just catch the exception and output a friendlier message.

If not, we may have some work to do - although I'd suggest not holding
up 1.7 for it.

[1]: http://sourceforge.net/tracker/index.php?func=detail&aid=1763338&group_id=153041&atid=790198

-- 
----
Waylan Limberg
wa...@gm...