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We’ve just finished building a site that is aimed largely at users with disabilities, and as a result we did quite a bit of testing with the Jaws screen reader to see how the site appears to a blind user.

I got into quite a fight with Jaws, Javascript and bad magic.  I was adding some Javascript to modify a Wysiwyg editor to make it a bit more screen-reader friendly.  At first it seemed that the Javascript just wasn’t working, but further playing revealed that it was but that Jaws wasn’t seeing the modifications that Javascript had made to the page, which was odd, as Jaws was able to see the Wysiwyg editor which itself had been created by Javascript  And sometimes the Javascript just made Jaws read out the text for one link when the keyboard focus was clearly on another.

It turns out that (apparently) Jaws scans the web page when it finishes loading and creates its own copy of the elements on the page, so that when the user tabs through the items on the page Jaws tabs through its own copy of the page and reads out the elements.

Tbe problem is that a lot of Javascript gets run at page load time, (either because the <script> tags have been put at the end of the body, or because there’s some kind of jQuery type $(document).ready() thing in use).  And it’s at page load time that Jaws makes its secret copy of your page.  So if your Javascript is fast enough then it will run before Jaws reads the page, but if it’s too slow then Jaws wont know about the changes to the page, and so when your user tabs through the items on the page Jaws will read out the item that it thinks is there, even if it’s not.

It occurred to me a while ago that it must be possible to get into PDB in a Zope page template by using the ‘python:’ TALE and the magic ‘modules’ variable that is available there.  And you can!  It’s really dirty, but I’m sure it must be possible to do something useful with it:

<tal:x define=”x python:modules['pdb'].set_trace()” />

When the page is loaded it successfully drops you into the Python Debugger in the terminal, but it seems to be in some kind of context-less, etherial, undefined mystery state in which you can’t access any of the things that you would normally be able to access with python in a tal template.

Can anyone take this a step further and get it to be useful?

Just like in normal Python, in Zope’s restricted Python you can use isinstance(var, type) to detect if a variable is of the given type or not:

>>> print isinstance(‘my string’, str)
>>> True

Which works fine.  But then you try this:

>>> print isinstance(['my','list'], list)
>>> TypeError: isinstance() arg 2 must be a class, type, or tuple of classes and types

WTF?

For some reason it doesn’t like the list type.  You can use str or int, but not list.  I’m still not sure why this is, and right now I don’t have the time to find out.  But the alternative solution is to use Zope Python’s same_type function.

>>> print same_type(['my','list'], list)
>>> True