def validate(self, value, model=None, context=None):
import re<EOL>value = str(value)<EOL>match = re.match(r'<STR_LIT>', value)<EOL>if not match or value != match.group():<EOL><INDENT>return Error(self.not_digital)<EOL><DEDENT>return Error()<EOL>
Validate
Perform value validation and return result

:param value:           value to check, cast to string
:param model:           parent model being validated
:param context:         object or None, validation context
:return:                shiftschema.results.SimpleResult