CommaStringMultipleChoiceField - store multiple values as a comma-delimited string in Django

comma_string_multiple_choice_field.py

class CommaStringMultipleChoiceField(MultipleChoiceField):

    def to_python(self, value):
        if isinstance(value,str):
            return [val.rstrip().lstrip() for val in value.split(',')]
        else:
            return []
    
    def prepare_value(self, value):
        return self.to_python(value)

    def clean(self, value):
        self.validate(value)
        if isinstance(value, (list, tuple)):
            return ",".join([val.rstrip().lstrip() for val in value])
        else:
            return ''