desc silently fails if it doesn't handle the argument

[nburns]

Found this strange behavior:
Descending (note the lack of a DESC in the output:

ipdb> select(t for t in ReplyTemplate).order_by(desc(lambda t: t.id)).get_sql()
'SELECT DISTINCT `t-1`.`id`, `t-1`.`enabled`, `t-1`.`company`, `t-1`.`kind`, `t-1`.`created_by`, `t-1`.`modified_by`, `t-1`.`title`, `t-1`.`body`, `t-1`.`display_order`, `t-1`.`time_created`, `t-1`.`time_modified`, `t-1`.`shadowed_system_template`\nFROM `reply_template` `t-1`\nORDER BY `t-1`.`id`'

Nothing (ascending)

ipdb> select(t for t in ReplyTemplate).order_by(lambda t: t.id).get_sql()
'SELECT DISTINCT `t-1`.`id`, `t-1`.`enabled`, `t-1`.`company`, `t-1`.`kind`, `t-1`.`created_by`, `t-1`.`modified_by`, `t-1`.`title`, `t-1`.`body`, `t-1`.`display_order`, `t-1`.`time_created`, `t-1`.`time_modified`, `t-1`.`shadowed_system_template`\nFROM `reply_template` `t-1`\nORDER BY `t-1`.`id`'

looking at the source of desc:

def desc(expr):
    if isinstance(expr, Attribute):
        return expr.desc
    if isinstance(expr, DescWrapper):
        return expr.attr
    if isinstance(expr, int_types):
        return -expr
    if isinstance(expr, basestring):
        return 'desc(%s)' % expr
    return expr

It looks like this is intended? Can you help me understand why it behaves like this?

[sashaaero]

Hello!
The correct usage in your case would be either

select(t for t in ReplyTemplate).order_by(lambda t: desc(t.id)).get_sql()

or

select(t for t in ReplyTemplate).order_by(desc(ReplyTemplate.id))

[nburns]

Thanks for taking a look and thanks for the response!

What do you think about something like raising if callable(expr)?

Also happy to do a PR just wanted to talk through it first so it wasn't a surprise or never got reviewed.