Does Buildout support value substitution in the extends option?

Question

Does Buildout support value substitution in the extends option of the buildout section?

For example, this example.cfg doesn't extend with base.cfg:

[config]
base = base.cfg

[buildout]
extends =
    ${config:base}
parts =

---

buildout -c example.cfg annotate

---

My goal is to send the file-to-extend as a parameter from the outside like this:

buildout config:base=base.cfg -c example.cfg annotate

I tried to merge the buildout:extends from the outside; but that doesn't work either:

buildout buildout:extends+=base.cfg -c example.cfg annotate

Mennonite

Since I am writing everything in a bash script, I did template substitution using envsubst to get the same effect. Probably, I need to switch to Python though. – Mennonite

Answer 1

No, extends doesn't support value substitutions, unfortunately. The current implementation processes buildout.extends before variable substitution can take place.

There is an existing feature request open for this: #39 No variable substitutions in extends.

I generally create a local.cfg file first, perhaps from a template, and run buildout -c local.cfg. That'd be the kind of place I'd put custom extends configuration.

Perineum

Thanks, I had a feeling that order matters for extends. Need to dig deeper into the code though. – Mennonite

@Nishant: extends is handled inside _open(). _open() is called to load the configuration file for the Buildout() instance, which eventually sets self._raw from the merged results. – Perineum

@Nishant: self._raw is used in __getitem__ to create Options() instances per section, and only then, in Options._initialize(), are value substitutions processed. – Perineum

I did check this meta.stackexchange.com/questions/77226/…, but I can't figure out how to offer extra points. – Mennonite

How do I offer extra bounties for this answer? This was like a tip of iceberg for me and I was given a proper answer including GitHub PR for an existing question. Is there some way to offer some bounties like 100 points for this answer? – Mennonite

@Mennonite I’m glad you found this to be helpful! See Can't we award bounty to a helpful answer directly? for the details on how you can award a bounty to an existing answer. – Perineum

Thanks, @Martijn! I have added a bounty. – Mennonite