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

[Jason B. <jb...@ze...>]

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?  :-)