Re: [Configobj-develop] Can I get a value through the interpolation path?

[Entity R. <ent...@gm...>]

On Wed, 2010-03-17 at 14:53 -0500, Jason Baker wrote:
> On Wed, Mar 17, 2010 at 1:52 PM, Michael Foord
> <fuz...@vo...> wrote:
>         
>         
>         Well - as far as I can tell setdefault is exactly a "magical
>         get_by_interpolation function" - so I guess I'm not
>         understanding you (setdefault is also a standard dictionary
>         method).
>         
>         Michael
> 
> Consider the following config file:
> 
> [section]
> foo = 'bar'
>   [[subsection]]
>   baz =  '$foo'
> 
> Suppose I have a Section object that represents the subsection
> (configobj['section']['subsection']).  Now suppose I do this:
> 
> a = subsection['baz']
> 
> Since the option baz contains a string '$foo', what happens is
> something like the following:
> 
>  1. The interpolater looks in subsection to see if it has a foo
> option.
>  2. When it sees that it doesn't exist, it checks the DEFAULT section.
>  3. When it sees that *that* doesn't exist, it checks the parent
> section
>  4. The parent section has a foo option, so it returns it.
> 
> Now suppose I do this:
> 
> b = subsection['foo']
> 
> What happens is more like the following:
> 
>  1. Subsection is searched for a foo option.
>  2. Subsection doesn't have a foo option, so it throws a KeyError.
> 
> What I would like is some kind of function such that I can do
> something like this:
> 
> c = subsection.get_by_interpolation('foo')
> 
> ...that would look for an option named foo, but would look in the same
> places as the first operation.  Here's the reason why I want to do
> this.  Using envbuilder, I want to write a config file like this:
> 
> [project]
> parcel = 'parcel1', 'parcel2'
> 
>   [[DEFAULT]]
>   branch = 'master'
> 
>   [[parcel1]]
> 
>   [[parcel2]]
>   branch = 'someotherbranch'
> 
> [commands]
>   [[update]]
>   default = 'git pull origin %branch'
> 
> Essentially, I've written my own interpolation engine for commands
> such that a variable beginning with % is to be on the parcel.  So when
> I run "envb update", it should essentially run:
> 
> # Get parcel1 using branch from default
> $ git pull origin master
> 
> # Get parcel2 using branch from parcel2
> $ git pull origin someotherbranch
> 
> However, parcel1 would throw an exception because it doesn't actually
> have an option named "branch".  Of course, I could do something like
> this:
> 
> [project]
> parcels = 'parcel1', 'parcel2'
> 
>   [[DEFAULT]]
>   default_branch = 'master'
> 
>   [[parcel1]]
>   branch = '$default_branch'
> 
>   [[parcel2]]
>   branch = 'someotherbranch'
> 
> [commands]
>   [[update]]
>   default = 'git pull origin %branch'
> 
> ...but that gets tedious when you start dealing with a nontrivial
> amount of parcels.
> 
> Does that make things more clear, or did I just confuse you even
> more?  :-)
> 
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I as well am interested in this. Auto-interpolation of a tree of
sections. Or rather, start from a specified branch, and then percolate
towards the trunk until a valid variable is found.

My Example: (IRC Bot)
[servers]
    nick = BarBaz
    # ...
    [[Freenode]]
        nick = FooBar
        # ...
    [[EFNet]]
        # ...

config['servers']['EFNet'] (or some similar syntax) would return
"BarBaz"