Add override-flag to dotenv_values to allow for more advanced chaining

Author: johnbergvall

Diff for: CHANGELOG.md

@@ -11,6 +11,8 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 - Add support to use a custom dict instead of os.environ for variable
   interpolating when calling `dotenv_values` (by [@johnbergvall])
+- Add override-flag to `dotenv_values` to allow for more advanced
+  chaining of env-files (#73 #186 by [@johnbergvall])
 
 ## [0.19.0] - 2021-07-24
 

Diff for: README.md

@@ -110,7 +110,8 @@ deploy_env = {
   'VERSION': '1.5',
 }
 env = dotenv_values('.env.deployment01', base_env={
-    **dotenv_values('.env.base', base_env=deploy_env),
+    # override=False to ignore local file overrides in interpolations:
+    **dotenv_values('.env.base', override=False, base_env=deploy_env),
     **deploy_env,
 })
 subprocess.call(

Diff for: src/dotenv/main.py

@@ -337,6 +337,7 @@ def dotenv_values(
     dotenv_path: Union[str, _PathLike, None] = None,
     stream: Optional[IO[str]] = None,
     verbose: bool = False,
+    override: bool = True,
     interpolate: bool = True,
     encoding: Optional[str] = "utf-8",
     base_env: Mapping[str, Optional[str]] = os.environ,
@@ -348,6 +349,8 @@ def dotenv_values(
     - *stream*: `StringIO` object with .env content, used if `dotenv_path` is `None`.
     - *verbose*: whether to output a warning the .env file is missing. Defaults to
       `False`.
+    - *override*: whether to override the system environment/`base_env` variables with
+      the variables in `.env` file. Defaults to `True` as opposed to `load_dotenv`.
     - *encoding*: encoding to be used to read the file.
     - *base_env*: dict with initial environment. Defaults to os.environ
 
@@ -361,7 +364,7 @@ def dotenv_values(
         stream=stream,
         verbose=verbose,
         interpolate=interpolate,
-        override=True,
+        override=override,
         encoding=encoding,
         base_env=base_env,
     ).dict()