Error handling with Python + Pylons

Question

What is the correct way to handle errors using Python + Pylons?

Say that the user enters the password through the form, which when passing the model class through the controller gives an error, because it is too short. How should this error be handled so that the error message is displayed on the web page and not the entire script ending on the error page?

Should there be any errors in the controller itself?

I hope I explain clearly.

Thank.

Answer 1

? formalchemy. . , .

.

Answer 2

formencode @validate decorator. , , , .

, formencode, c.form_errors.

Answer 3

, . pylons.decorators:

from decorator import decorator
from webob import UnicodeMultiDict

class ModelException(Exception):
    pass

def handle_exceptions(form):
    def wrapper(fn, self, *args,**kwargs):
        try:
            return fn(self, *args, **kwargs)
        except ModelException, e:
            errors = str(e)
            params = request.POST

            is_unicode_params = isinstance(params, UnicodeMultiDict)
            params = params.mixed()


            request.environ['pylons.routes_dict']['action'] = form
            response = self._dispatch_call()
            # XXX: Legacy WSGIResponse support
            legacy_response = False
            if hasattr(response, 'content'):
                form_content = ''.join(response.content)
                legacy_response = True
            else:
                form_content = response
                response = self._py_object.response

            # If the form_content is an exception response, return it
            if hasattr(form_content, '_exception'):
                return form_content

            form_content = htmlfill.render(form_content, defaults=params,
                                           errors=errors)
            if legacy_response:
                # Let the Controller merge the legacy response
                response.content = form_content
                return response
            else:
                return form_content
    return decorator(wrapper)


class HelloFormSchema(Schema):
    allow_extra_fields = True
    filter_extra_fields = True
    name = formencode.validators.UnicodeString(not_empty=True)
    email = formencode.validators.UnicodeString(not_empty=True)

class HelloController(BaseController):
    def new(self):
        return render('/hello/new.html')

    def view(self):
        return 'created'

    @handle_exceptions(form='new')
    @validate(schema=HelloFormSchema(), form='new')
    @restrict("POST")
    def create(self):
        #here is code interacting with model which potentially could raise exception:
        if self.form_result['name'] == 'doe':
            raise ModelException('user already exists!')
        return redirect(url(controller='hello', action='view'))

new.html:

${h.form(h.url(controller='hello', action='create'), 'post')}
<dl>
    <dt>Name</dt>
    <dd>${h.text('name')}</dd>
    <dt>Email</dt>
    <dd>${h.text('email')}</dd>
    <dd>
    ${h.submit('create', 'Create')}
    </dd>
</dl>
${h.end_form()}