[albatross-users] Newbie albatross question :)

[Cameron Blackwood]

<warning>More questions below... :) </warning>


Dave Cole writes In message <m3adkijkzu.fsf at ferret.object-craft.com.au>:
  | 
  | The "easy cgi's" is probably the most important thing about Albatross.
  | Building small to medium web applications which capture and process
  | complex user input is where Albatross is intended to shine.

*nod* Yep. Ive had to fight some things, but now I think I
have a handle on it.

One thing that I did spend __AGES__ on was trying to track
down :

  [Sun Nov 10 03:27:19 2002] [error] [client 10.0.0.1] Premature end of script headers: /home/httpd/cgi-bin/20c

It turns out that Id accidently deleted my:

  def page_display(s,ctx):
    ctx.run_template('login.html')

So albatross was processing my object and then displaying nothing.
Man, that sucked!! It took me about an hour to find. (I
deleted it as I cut and pasted some of my methods into a
parent class, so I thought it was that.)

Maybe albatross should return 'no output generated by object NAME'
or something from the flush()?  

I cant see any reason why you'd want to not return _anything_. 
Maybe an overwritable 'default/no output' return would be a good thing?

  | 
  | Cameron> I tried Random*App too, but have gone back to the simple.  I
  | Cameron> considered the Page stuff, but *shrugs* Ill change it if it's
  | Cameron> a problem. :)
  | 
  | Once you use server-side sessions you are able to mostly avoid using
  | forms to propagate state.  This means that the redirect becomes
  | useable again.


Actually I do have a question... 


step1
=====
Im using:

from albatross import SessionFileAppContext as Albatross_Context
from albatross import SimpleSessionFileApp as Albatross_Application
from albatross import SessionFileContextMixin   # <---to hack the content type
from albatross.cgiapp import Request

and Im finding that if i have an error in my code that makes
a traceback dump, then my state is lost. (IE, if i fix the
code and then hit reload (which then gives the warning about
'post'ing the data again), I am back to my login screen
(which is my startup page)).

Is this because my context is being saved as 'empty' because
   * the context is created at the start of the request 
   * my code is processed and bombs out
   * the empty context is saved? 
or something silly like that?

(Or would this problem go away if I use Client based state?
I just changed it to SimpleAppContext and now if I get an
error, I can reload the page and my state remains. Hmmm.)


step2
=====
Ok, Im dumb. :) 

It turns out that it was caused by my not setting 
ctx.add_session_vars in each 'create_context'.


step3
=====
Errr, ok maybe it wasnt that either.

Um. Ok. Confused now.

Somehow my context is being lost if I get a traceback (I put
a button which causes a divide by zero error in my code. If
I hit reload, then my login screen appears.

If I use SimpleAppContext rather than SessionFileAppContext
then my problem goes away (becuase the state is stored in
the form, so when I 'repost' it reloads the state, I guess)


Questions
=========
So, I guess Im asking what happens in the SessionFileAppContext
state then and how do I get around this?

And just to check, but I dont need to add create_context()
each create_context() do I? Once it's in the state it's
there for good?


  | 
  | Cameron> One annoyance I found in changing, is that the keywords used
  | Cameron> by the __init__ of the App classes wont accept keywords from
  | Cameron> other App classes.
  | 
  | Hmmm...  I am not sure that there is much we can do about that without
  | introducing very hard to find problems.

Well the documentation uses the form:
 ModularSessionApp.__init__(self,
                      base_url = 'popview.py',
                      module_path = '.',
                      template_path = '.',
                      start_page = 'login',
                      secret = '-=-secret-=-',
                      session_appid = 'popview4')


Ok, this us ugly, so stick with me here....

  def   __init__(self,*static_args,**keywords):
    static_arg_names=[  'base_url', 'module_path', 'template_path', 
                        'start_page', 'secret', 'session_appid'
                     ]
    if len(static_args)>len(static_arg_names):
      print 'too many args... '
      sys.curl_up_and_die(-1)

    for i in range(len(static_args)):
      keywords[ static_arg_names[i] ]=static_args[i]
    for i in range(len(static_arg_names)):
      if not keywords.has_key: 
        print 'You didnt supply the arg',static_arg_names
        sys.curl_up_and_die(-1)
    base_url=keywords['base_url']
    secret=keywords['secret']
    template_path=keywords['template_path']
    # etc 
    # and then the standard __init__ code


So if people used:

   __init__(self,'popview.py','.','.','login','-=-secret-=-','popview4') 

or
   __init__(self, base_url = 'popview.py', module_path = '.', template_path = '.', start_page = 'login', secret = '-=-secret-=-', session_appid = 'popview4')

it should work fine in both cases.

_But_, if the same stuff is done to all the __init__
functions, then I could change the class from
SimpleSessionFileApp to SimpleApp and the extra args would
just be ignored (if i used the 2nd format!)

This would be a 'good thing' as it would mean you could
change storage systems easily. It should be transparent,
yeah?




  | Maybe the write_headers() method should write out a list/dictionary of
  | headers for which a default was established in the constructor.
  | During request processing all you would then need to do is alter the
  | headers.
  | 
  | Something like:
  | 
  |     ctx.set_header('Content-Type', 'image/png')

Yep. Im in heaven :) Perfect :)

  | 
  | - Dave
cam

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