launchpad-dev team mailing list archive

[Jonathan Lange <jml@xxxxxxxxxxxxx>]

On Thu, Feb 11, 2010 at 5:00 PM, Tom Berger <tom.berger@xxxxxxxxxxxxx> wrote:
> On 11 February 2010 16:51, Barry Warsaw <barry@xxxxxxxxxxxxx> wrote:
>> Just a quick plea:
>>
>> When writing new model objects, or touching existing ones, please think about
>> given them a useful __repr__().  This can greatly improve the introspection
>> experience when using pdb or 'make harness'.
>>
>> Many/most of our model classes have no repr which means when you look at an
>> object you get unhelpful output:
>>
>>    >>> ls = getUtility(ILanguageSet)
>>    >>> ls.get(123)
>>    <Language at 0x12345678>
>>
>> and then you have to find the class definition and go digging into various
>> attributes to figure out which object you have.  Wouldn't it be much nicer to
>> see:
>>
>>    >>> ls.get(123)
>>    <Language: French (fr)>
>>
>> with no further effort?
>>
>> It's easy to do, too.  E.g. I have a branch hopefully landing soon that adds
>> this to class Language:
>>
>>    def __repr__(self):
>>        return '<Language: %s>' % self.displayname
>>
>> A word of warning though: adding a repr to existing classes can break doctests
>> far from the models you're modifying, so land such branches through ec2.
>
> I like the example you gave above, but I have a couple of questions:
>
> 1. The default repr is unique. Should we try and preserve that?

As a rule of thumb, I try to have repr(a) == repr(b) <==> (a == b),
rather than (a is b). I don't know if that's standard or helps.

> 2. Is there a style guide for repr?

I don't know. Reckon we need one?

jml