# User Errors and Warnings

When processing a request, you can stop the flow by raising an exception that will be displayed to the user as an error message or a warning. They are respectively `UserError` and `UserWarning`.

## User Errors

An error displays a message and optionally a description to the user.

Example:

    from trytond.exceptions import UserError
    from trytond.model import Model

    class MyModel(Model):
        "My Model"
        __name__ = 'my_model'

        def process(self):
            if check_failed:
                raise UserError("You cannot process.", "because…")

Note

They are often used in combination with `gettext()` to translate the messages.

## User Warnings

A warning displays a confirmation message with optionally a description to the user. The user can decide to continue so the request is processed again without stopping at the warning. Otherwise the user can cancel its request. The warning instance is identified by a name which allows to skip it the next time it is checked, that’s why they often contain data like the id of a record.

Example:

    from trytond.exceptions import UserWarning
    from trytond.model import Model
    from trytond.pool import Pool

    class MyModel(Model):
        "My Model"
        __name__ = 'my_model'

        def process(self):
            Warning = Pool().get('res.user.warning')
            warning_name = 'mywarning,%s' % self
            if Warning.check(warning_name):
                raise UserWarning(warning_name, "Process cannot be canceled.")

Note

If there is no user interaction the warnings can be skipped by setting the `_skip_warnings` key of the context to `True`.