Re: [Fab-user] external role definitions

[Jeff Forcier]

Hi Michael,

Apologies for the long delay, been busy :(

I just made a ticket for this to keep it from getting buried in my inbox:

    http://code.fabfile.org/issues/show/266

I'll need more time to think about how I see the feature fitting into
Fabric overall, but the overall concept (an easy way to fill the
roledefs from external sources instead of defining it in Python) is
definitely something I think we should have eventually.

I'd expect to be looking at this for Fab 1.1 or 1.2 when we start
doing more serious work with OO tasks/roles/hosts/etc, as it fits
neatly into that sort of effort.

Best,
Jeff

On Fri, Nov 19, 2010 at 4:53 AM, Michael Gliwinski
<address@hidden> wrote:
> On Friday 19 Nov 2010 02:41:28 Jeff Forcier wrote:
>> Hey Michael,
>>
>> As Morgan said, we'd love to see what you have, for sure! A couple
>> additional points below.
>
> OK, I don't have it anywhere public, it's really just few lines of code, so
> pasted them below.
>
> [...]
>> I'm not sure how much of the Fab source you peeked at, but roledefs
>> are already lazy, so hopefully your load_from() method is just
>> populating the dict values with callables -- that's all that should be
>> necessary for this aspect of your setup to work, off the top of my
>> head.
>
> Yes, I knew about that, but in this case I'm actually loading the whole dict
> instead of each role individually.  I think it would actually be more
> complicated to try to split it, but see below.
>
> [...]
>> That's certainly valid. Part of me says the feature is a bit on the
>> esoteric side, but on the other hand I've always been a fan of adding
>> "power user" features provided the common use case isn't compromised
>> and said feature doesn't add significant complexity. Based on your
>> description, your change probably passes both those tests :)
>
> Well, my use case probably is, but I'm thinking that this can be used for as
> simple thing as just separating role definitions into another file.
>
>> Let us know where we can check it out and I'm sure we can offer
>> further advice/questions/etc, and if it looks good I'll definitely add
>> a ticket for figuring out how best to include it.
>
> Well, here goes (stripped most docstrings for brevity):
>
>
> from os import path
>
> import contextlib
> import functools
> import urllib2
> import urlparse
>
> import yaml
>
> def urlopen(url, *args, **kwargs):
>    """Open URL and return a file-like object for its resource.
>
>    This is just a wrapper for urllib2.urlopen to handle local paths (URLs
>    without scheme) and make the returned object behave like a context
> manager.
>    """
>    if not urlparse.urlsplit(url).scheme:
>        url = 'file://' + path.abspath(path.normpath(path.expanduser(url)))
>    return contextlib.closing(urllib2.urlopen(url, *args, **kwargs))
>
> class RoleDefs(dict):
>    _loaded = False
>    _sources = None
>
>    def load_from(self, sources):
>        if isinstance(sources, basestring) \
>           or not hasattr(sources, '__iter__'):
>            sources = [sources]
>        self._sources = sources
>
>   address@hidden
>    def source_loader(url):
>        with urlopen(url, 'r') as fp:
>            return yaml.load(fp)
>
>    def __missing__(self, key):
>        if self._loaded or not self._sources: raise KeyError(key)
>        self._loaded = True
>        sources = list(self._sources)
>        while sources:
>            src = sources.pop(0)
>            loader = src
>            if not callable(src):
>                loader = functools.partial(self.source_loader, src)
>            try:
>                self.update(loader())
>                break
>            except Exception:
>                if not sources: raise KeyError(key)
>        return self[key]
>
>
> --
> Michael Gliwinski
> Henderson Group Information Services
> 9-11 Hightown Avenue, Newtownabby, BT36 4RT
> Phone: 028 9034 3319
>
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-- 
Jeff Forcier
Unix sysadmin; Python/Ruby engineer
http://bitprophet.org