The core logic looks something like this:

from starlette.config import Config

config = Config(".env")

env1 = config("ENV1")

For local development, I would use an env file named .env with the variables I needed to avoid needing to manage environment variables.
For containerized deployments, I would define the needed environment variables and would not have the .env file.

Now (following #2422), those containerized deployments fail with a FileNotFoundError.

Essentially, things have switched from "fail slow, only if lookup fails" (as described in the configuration precedence section of the documentation) to "fail fast, if a specified file is missing".

I understand the motivation for the change (the author described it in #2101). However, couldn't the same effect be accomplished using a default False (or even default True if needed) check_file (arbitrary name for this example) keyword argument to Config like the below?

class Config:
    def __init__(
        self,
        env_file: typing.Optional[typing.Union[str, Path]] = None,
        environ: typing.Mapping[str, str] = environ,
        env_prefix: str = "",
+       *,
+       check_file: bool = False,
    ) -> None:
        self.environ = environ
        self.env_prefix = env_prefix
        self.file_values: typing.Dict[str, str] = {}
        if env_file is not None:
-           if not os.path.isfile(env_file):
+           if os.path.isfile(env_file):
+               self.file_values = self._read_file(env_file)
+           elif check_file:
                raise FileNotFoundError(f"Config file '{env_file}' not found.")
-           self.file_values = self._read_file(env_file)

This would allow the new error to be surfaced for those who want it without requiring it for those who don't.

Can you do the following?

try:
    config = Config(".env")
except FileNotFoundError:
    config = Config()

I could, but that would require a code change in any application following the previously-working (and documentation-approved) pattern. 🥲