repro: Cannot interpolate data of type 'list'

[TheFirstMe]

This is a sample of my dvc.yaml.

stages:
    train:
        cmd: python train.py --list ${base.list}

and my params.yaml looks like this:

base:
    loglevel: INFO
    list: ['a', 'b', 'c']
    random_key: random_value

dvc repro currently results in this error:

ERROR: failed to parse 'stages.train.cmd' in 'dvc.yaml':              
Cannot interpolate data of type 'list'

The expected command is python train.py --list 'a' 'b' 'c'

[pmrowla]

Related: #6107

[daavoo]

@TheFirstMe You can workaround this with https://dvc.org/doc/user-guide/project-structure/dvcyaml-files#dict-unpacking if you wrap the list inside a dict:

dict:
    list: ['a', 'b', 'c']

stages:
    train:
        cmd: python train.py ${dict}

[TheFirstMe]

@TheFirstMe You can workaround this with https://dvc.org/doc/user-guide/project-structure/dvcyaml-files#dict-unpacking if you wrap the list inside a dict:

dict:
    list: ['a', 'b', 'c']

stages:
    train:
        cmd: python train.py ${dict}

Yes, I am currently doing something like this. But the parameter list is something that will be accessed by multiple stages so I wanted to keep it under a common section (base).

[CarMiranda]

@TheFirstMe does something like the following serves your purpose?

# params.yaml
base:
  loglevel: INFO
  list:
    list: ['a', 'b', 'c']
  random-key: 0.1

stage1:
  param1: 0.1
  param2: 0.2
  param3: 0.3

stage2:
  param1: 0.3
  param2: 0.2

# dvc.yaml
stages:
  stage1:
    cmd: >-
      python script.py
      ${stage1}
      ${base.list}
      --random-key ${base.random-key}
      --log-level ${base.loglevel}
    deps:
      - script.py
  stage2:
    cmd: >-
      python script.py
      ${stage2}
      ${base.list}
      --random-key ${base.random-key}
      --log-level ${base.loglevel}
    deps:
      - script.py

As you can see, the common parameters remain under the base key, but list is replaced by list: list: [...] which allows to interpolate in the common manner. However, in this way, one cannot expect to interpolate ${base}, which is why the other parameters are specified in the commands.

If you really do not want to write the other parameters, you can simply group them in another key, within the same (or another) dictionary:

base:
  list:
    list: ['a', 'b', 'c']
  others:
    log-level: INFO
    random-key: 0.1

# ...

stages:
  stage1:
    cmd: >-
      python script.py
      ${stage1}
      ${base.list}
      ${base.others}
    deps:
      - script.py
# ...

This is a workaround, I would expect for plain list interpolation to land some time in the (near?) future.