def get_printable_field_value(instance, fieldname):
    """ Get the display value of a model field, showing a comma-delimited
        list for M2M fields.
    """
    field = instance._meta.get_field(fieldname)
    field_value = getattr(instance, fieldname)

    if isinstance(field, models.ManyToManyField):
        field_value = ', '.join([unicode(f) for f in
                    field_value.all()])
    return field_value