OmegaConf 2.1: changes in DictConfig __getitem__ and __getattr__

[omry]

An historical decision was to make __getitem__ and __getattr__ return None if a the input key is not found.
This is inconsistent with the behavior of plain dict and regular Python objects.

Fixing this is a breaking change, users depending on it will need small code changes.

Accessing a non existing attribute

In general,

cfg.some_attribute
# and
cfg["some_attribute"]

Can be replaced with:

cfg.get("some_attribute")
# or
getattr(cfg, "some_attribute", None)

Depending on the type annotation of cfg, one may be more appropriate than the other, but both will work.

Checking if an attribute exists

If the context of your usage is is existence check, you can also use:

if cfg["some_attribute"] is not None:
   ...

And

if cfg.some_attribute is not None:
   ...

Will have to be replaced with

if "some_attribute" in cfg:
  ...

Note that is cfg is ducktyped as a type, you can use hasattr just like you would on an real instance of Config:

def foo(cfg: Config):
  # before
  if cfg.some_attribute is not None: 
    ..
  # after
  if hasattr(cfg, "some_attribute"):
    ...

Note:
DictConfig put into struct mode is already behaving in the new way (raising exceptions).
This change should not affect most Hydra users because Hydra puts the cfg object into struct mode by default.