Node interpolation

An interpolation stores an expression and evaluates it when you read the value. ${server.port} reads another node in the same config:

>>> from omegaconf import OmegaConf
>>> cfg = OmegaConf.create({
...     "server": {
...         "host": "localhost",
...         "port": 80,
...     },
...     "client": {
...         "port": "${server.port}",
...         "url": "http://${server.host}:${server.port}",
...     },
... })
>>> cfg.client.port
80
>>> cfg.server.port = 8080
>>> cfg.client.port
8080

An interpolation occupying the whole value retains the referenced value's type, so cfg.client.port is an integer. Embedding node references in text produces a string:

>>> cfg.client.url
'http://localhost:8080'

Paths may use dots or brackets; escape special characters when they belong to a key rather than the path. See the interpolation grammar for the complete syntax.

Relative references

One leading dot starts at the current container; each additional dot moves up one level:

>>> cfg = OmegaConf.create({
...     "server": {
...         "port": 80,
...         "selected": "${.port}",
...     },
... })
>>> cfg.server.selected
80

Nested references

An interpolation can select part of another interpolation's path:

>>> cfg = OmegaConf.create({
...     "plans": {
...         "A": "plan A",
...         "B": "plan B",
...     },
...     "selected": "A",
...     "plan": "${plans[${selected}]}",
... })
>>> cfg.plan
'plan A'
>>> cfg.selected = "B"
>>> cfg.plan
'plan B'

Avoid cycles: an interpolation cannot eventually refer back to itself.

Resolve now

OmegaConf.resolve(cfg) replaces interpolations in a config with their resolved values. This is useful before passing data to code that should not depend on later config changes. It mutates the config, so copy it first if you need to keep the original lazy expressions.

Next, learn how resolver calls compute values instead of referencing another node.