[Twisted-web] Rendering error messages

[Michael Wilson]

I have a form where the inputs various values, which I then check for
validity. If there are errors, I'd like to re-display the form, with
errors.

>From the examples, I see how to use pasting to get the error into the form:

....
            <td>School name:</td>
            <td>&nbsp;&nbsp;</td>
            <td><input type="text" name="name" /></td>
            <td><nevow:slot name="nameError">error</nevow:slot></td>
....

	def render_aPasting(self, context, data):
			context.tag.fillSlots('nameError', self.nameError)

----

That works great. The problem is, I initialize self.nameError in __init__:

self.nameError = ''

And then set it in the formless autocall if there is an error:

-----

		if self.schoolDb.exists( name ):
			self.nameError	= 'School already exists!'
			return
----

The problem is that when the page is re-rendered, __init__ is being
called again, which means the errors get cleared.

My instinct is that maybe I should use session variables, but before I
got an do that I wanted to make sure there wasn't another, more
correct way to do this.

Thanks!