Support for KARTON_CONFIG_FILE env variable for providing configuration file path

docs/service_configuration.rst

@@ -25,6 +25,7 @@ Configuration values are read from various sources using the following precedenc
 - ``/etc/karton/karton.ini`` file (global)
 - ``~/.config/karton/karton.ini`` file (user local)
 - ``./karton.ini`` file (subsystem local)
+- path provided via ``KARTON_CONFIG_FILE`` environment variable
 - ``--config-path <path>`` optional, additional path provided in arguments
 - ``KARTON_SECTION_OPTION`` values from environment variables e.g. (``secret_key`` option in ``[s3]`` section can be overridden using ``KARTON_S3_SECRET_KEY`` variable)
 - Command-line arguments (if ``Karton.main()`` method is used as entrypoint)

karton/core/config.py

@@ -14,6 +14,7 @@ class Config(object):
     - ``/etc/karton/karton.ini`` (global)
     - ``~/.config/karton/karton.ini`` (user local)
     - ``./karton.ini`` (subsystem local)
+    - path from ``KARTON_CONFIG_FILE`` environment variable
     - ``<path>`` optional, additional path provided in arguments
 
     It is also possible to pass configuration via environment variables.
@@ -38,6 +39,12 @@ def __init__(
     ) -> None:
         self._config: Dict[str, Dict[str, Any]] = {}
 
+        path_from_env = os.getenv("KARTON_CONFIG_FILE")
+        if path_from_env:
+            if not os.path.isfile(path_from_env):
+                raise IOError(f"Configuration file not found in {path_from_env}")
+            self.SEARCH_PATHS = self.SEARCH_PATHS + [path_from_env]
+
         if path is not None:
             if not os.path.isfile(path):
                 raise IOError("Configuration file not found in " + path)