A form has a field. The field has a validator. The validator calls a parser. If and only if the parsing succeeds, the validation is successful. However, later I have to call the parser again to get the parsed value. How can I avoid this duplication? Should I attach the result to the field object as a new attribute? Simplified Flask code: def data_validator(form, field): try: result = parse(field.data) # <-- first parser call, but the result will be lost except Exception as err: raise ValidationError(f"Invalid data: {err}") from None class DataForm(FlaskForm): datafield = wtf.fields.StringField('Enter data', validators=[data_validator]) ... @app.post('/some/url') def view_function(): form = DataForm() if form.validate_on_submit(): result = parse(form.datafield.data) # <-- second parser call ... Continue reading...
