deform_show_error_near_field.py

# schema

class LoginSchema(Schema):
    login = SchemaNode(
        String(),
        title='Login',
        widget=TextInputWidget(),
    )

    password = SchemaNode(
        String(),
        title='Password',
        widget=PasswordWidget(),
    )

# sub function

def exception_for_form_field(form, field_name, text):
    exc = colander.Invalid(form)
    """:type : SchemaNode"""
    field = form.get(field_name)
    exc.add(colander.Invalid(field, text), field._order)
    return exc


# validator

        def validate_auth(form, values):
            nonlocal authed_user

            login = values.get('login')
            password = values.get('password')
            user = User.by_any(login)
            if not user:
                raise exception_for_form_field(form, 'login', 'User not found')
            if not user.check_password(password):
                raise exception_for_form_field(form, 'password', 'Wrong password')

            authed_user = user

# form creation

        login_form = Form(
            LoginSchema(validator=validate_auth),
            buttons=[Button(name='login_form_submit', title='Enter')]
        )