Common variables?

[FeryET]

Image I have two objects that depend on the same value, but I want to keep a good dependency injection pattern without too much of a manual coding.

class A:
   def __init__(today: str):
        self.today = today

class B:
  def __init__(today: str):
       self.today = today

Both of these classes have their own config files. How can I keep today consistent between these two? Does hydra provide any solution? jsonargparse has a feature that you can link two variables together. It would be neat to see if hydra provides similar configurability.

[Jasha10]

See OmegaConf's variable interpolation feature.

Are you using Hydra's instantiate API? If so, something like this should work:

# my_config.yaml
a_instance:
  _target_: my_module.A
  today: ${today}
b_instance:
  _target_: my_module.B
  today: ${today}
today: ...

The string "${today}" is a "variable interpolation". It essentially functions as a pointer to the top-level "today" key.

[aliutkus]

Would this thing work if I wanted today to be an object ?

I actually want:

c_instance = my_module.C(params_c=3)
a_instance = my_module.A(params_a=1, c_instance=c_instance)
b_instance = my_module.B(params_b=1, c_instance=c_instance)

Is this doable with hydra, e.g. with something like:

# my_config.yaml
a_instance:
  _target_: my_module.A
  params_a: 1
  c_instance: ${c_instance}
b_instance:
  _target_: my_module.B
  param_b: 2
  c_instance: ${c_instance}
c_instance:
  _target_: my_module.C
  param_c: 3

thanks

[Jasha10]

This can work, though with the current implementation the a_instance.c_instance will not refer to the same object as the top-level c_instance.

Here is a demo:

# my_module.py
class A:
    def __init__(self, params_a, c_instance):
        self.params_a = params_a
        self.c_instance = c_instance

class B:
    def __init__(self, params_b, c_instance):
        self.params_b = params_b
        self.c_instance = c_instance

class C:
    def __init__(self, params_c):
        self.params_c = params_c

# app.py
from hydra.utils import instantiate
from omegaconf import OmegaConf

yaml_data = """
# my_config.yaml
a_instance:
  _target_: my_module.A
  params_a: 1
  c_instance: ${c_instance}
b_instance:
  _target_: my_module.B
  params_b: 2
  c_instance: ${c_instance}
c_instance:
  _target_: my_module.C
  params_c: 3
"""

cfg = OmegaConf.create(yaml_data)

out = instantiate(cfg)

# The objects have the correct type:
from my_module import A, C
assert isinstance(out.a_instance, A)
assert isinstance(out.a_instance.c_instance, C)
assert isinstance(out.c_instance, C)

# However, the identity of the objects is not the same:
assert id(out.a_instance.c_instance) != id(out.c_instance)

There is an open feature request to implement dependency injection with the same object identity (i.e. to get id(out.a_instance.c_instance) == id(out.c_instance)): #1393.

[aliutkus]

Thanks a lot for your answer. This feature request is indeed exactly what I need and it would be a super awesome feature.