Node and string interpolation

Node interpolation references another value in the config. OmegaConf resolves interpolations lazily, when you access the value. ${server.port} references the server.port node:

>>> 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

A node interpolation occupying the whole value retains the referenced value's type, so cfg.client.port is an integer.

String interpolation

String interpolation combines interpolation expressions with literal text to produce 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.

For resolved YAML output while preserving the config's interpolations, use OmegaConf.to_yaml(cfg, resolve=True). See Convert config to YAML for a comparison with the default unresolved output.

Next, learn how resolver interpolation computes values instead of referencing another node.