def validate(self):
for name, col in self._columns.items():<EOL><INDENT>v = getattr(self, name)<EOL>if v is None and not self._values[name].explicit and col.has_default:<EOL><INDENT>v = col.get_default()<EOL><DEDENT>val = col.validate(v)<EOL>setattr(self, name, val)<EOL><DEDENT>
Cleans and validates the field values