Simplest way to handle and display errors in a Python Pylons controller without a helper class

Question

I have a class User() that throw exceptions when attributes are incorrectly set. I am currently passing the exceptions from the models through the controller to the templates by essentially catching exceptions two times for each variable.

Is this a correct way of doing it? Is there a better (but still simple) way? I prefer not to use any third party error or form handlers due to the extensive database queries we already have in place in our classes.

Furthermore, how can I "stop" the chain of processing in the class if one of the values is invalid? Is there like a "break" syntax or something?

Thanks.

>>> u = User()
>>> u.name = 'Jason Mendez'
>>> u.password = '1234'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "topic/model/user.py", line 79, in password
    return self._password
ValueError: Your password must be greater than 6 characters

In my controller "register," I have:

class RegisterController(BaseController):

    def index(self):
        if request.POST:
            c.errors = {}
            u = User()

            try:
                u.name = c.name = request.POST['name']
            except ValueError, error:
                c.errors['name'] = error

            try:
                u.email = c.email = request.POST['email']
            except ValueError, error:
                c.errors['email'] = error

            try:
                u.password = c.password = request.POST['password']
            except ValueError, error:
                c.errors['password'] = error

            try:
                u.commit()
            except ValueError, error:
                pass

        return render('/register.mako')

Answer 1

You could remove repetition from the code as a semi-measure:

class RegisterController(BaseController):

    def index(self):
        if request.POST:
            c.errors = {}
            u = User()
            for key in "name email password".split():
                try:
                    value = request.POST[key]
                    for o in (u, c):
                        setattr(o, key, value)
                except ValueError, error:
                    c.errors[key] = error

            u.commit() # allow to propagate (show 500 on error if no middleware)

        return render('/register.mako')

Form Handling page from Pylons docs describes several simple approaches to form validating that you could adapt for your project.

class RegisterController(BaseController):

    @save(User, commit=True)
    # `save` uses filled c.form_result to create User() 
    @validate(schema=register_schema, form='register')
    # `validate` fills c.form_errors, c.form_result dictionaries
    def create(self):
        return render('/register.mako')

Where validate() is similar to Pylons validate() decorator and save() could be implemented as follows (using decorator module):

def save(klass, commit=False):
    def call(action, *args, **kwargs):
        obj = klass()
        for attr in c.form_result:
            if attr in obj.setable_attrs():
               setattr(obj, attr, c.form_result[attr])
        if commit:
           obj.commit()
        return action(*args, **kwargs)
    return decorator.decorator(call)