Dumb Question/Bug

[Mark Billion]

Works Just Fine

def cli_add():

    try:

        db.client.au_usr.default = auth.user_id

    except:

        redirect(URL('index'))

    form = SQLFORM(db.client, fields = ['d_fn', 'd_ln', 'd_aka', 'd_ss'], labels = {'d_ss': 'Social Security', 'd_aka': 'Any Aliases', 'd_65': 'Older than 65'}).process(next=URL('clients'))    

    return dict(form=form)

BUT WHEN I MOVE THE FORM CALL INTO THE TRY LOOP:

def cli_add():

    try:

        db.client.au_usr.default = auth.user_id

        form = SQLFORM(db.client, fields = ['d_fn', 'd_ln', 'd_aka', 'd_ss'], labels = {'d_ss': 'Social Security', 'd_aka': 'Any Aliases', 'd_65': 'Older than 65'}).process(next=URL('clients'))    

    except:

        redirect(URL('index'))

    return dict(form=form)

The look fails into the except redirect.....

Any thoughts?

[Leonel Câmara]

Why are you using an except without specifying the exception? Anyway just do this:

@auth.requires_login()

def cli_add():

    db.client.au_usr.default = auth.user_id

    form = SQLFORM(db.client, fields = ['d_fn', 'd_ln', 'd_aka', 'd_ss'], labels = {'d_ss': 'Social Security', 'd_aka': 'Any Aliases', 'd_65': 'Older than 65'}).process(next=URL('clients'))    

    return dict(form=form)

[Mark Billion]

Why are you using an except without specifying the exception? Trying to catch all possible exceptions.  

[Niphlod]

are you aware that in web2py any HTTP is a subclass of exception ? Never, never, never use an exception without specifying what exception your code may raise.

[Anthony]

More specifically, when you provide the "next" argument to SQLFORM.process(), it ultimately calls redirect(), which raises an HTTP exception. If you put the .process() call inside a try/except, that HTTP exception will get caught, and in your case, you are then ignoring it. We should probably spell this out more clearly in the book.

You could instead do something like:

    except Exception as e:
        if isinstance(e, HTTP):
            raise e # re-raise the exception in case of a redirect
        redirect(URL('index'))

But generally it is much better to catch specific exceptions.

Anthony

[Mark Billion]

Thanks guys -- that makes a ton of sense.  I really appreciate it.  

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Mark M. Billion
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[Mark Billion]

Just two questions for my edification:

1. Why did HTTP get grouped into exceptions

2. Is there a security reason not to catch all non-http exceptions, ie except EXCEPTION

[Anthony]

On Friday, December 26, 2014 9:15:40 AM UTC-5, Mark Billion wrote:

Just two questions for my edification:

1. Why did HTTP get grouped into exceptions

By making HTTP an exception, this allows both the framework and app code to short-circuit a given response at any point and immediately return something (e.g., you can raise an HTTP exception in a model, and it will return without executing the controller or view).
 

2. Is there a security reason not to catch all non-http exceptions, ie except EXCEPTION

I don't think it's necessarily a security issue. It's just that you usually don't want to catch all exceptions, particularly if your code isn't doing anything to actually inspect and handle the exception. You could end up introducing silent failures and subtle bugs. It could be OK to catch all exceptions if your "except" block then does something with the exception, such as executing special error handling code or re-raising particular exceptions.

Anthony

[Mark Billion]

Awesome.  I really appreciate the help.

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Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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