Add cli_exit_on_error config option (#340)

Co-authored-by: Hasan Ramezani <hasan.r67@gmail.com>

Author: kschwab

docs/index.md

@@ -868,6 +868,28 @@ options:
 """
 ```
 
+#### Change Whether CLI Should Exit on Error
+
+Change whether the CLI internal parser will exit on error or raise a `SettingsError` exception by using
+`cli_exit_on_error`. By default, the CLI internal parser will exit on error.
+
+```py
+import sys
+
+from pydantic_settings import BaseSettings, SettingsError
+
+
+class Settings(BaseSettings, cli_parse_args=True, cli_exit_on_error=False): ...
+
+
+try:
+    sys.argv = ['example.py', '--bad-arg']
+    Settings()
+except SettingsError as e:
+    print(e)
+    #> error parsing CLI: unrecognized arguments: --bad-arg
+```
+
 #### Enforce Required Arguments at CLI
 
 Pydantic settings is designed to pull values in from various sources when instantating a model. This means a field that
@@ -884,10 +906,15 @@ import sys
 
 from pydantic import Field
 
-from pydantic_settings import BaseSettings
+from pydantic_settings import BaseSettings, SettingsError
 
 
-class Settings(BaseSettings, cli_parse_args=True, cli_enforce_required=True):
+class Settings(
+    BaseSettings,
+    cli_parse_args=True,
+    cli_enforce_required=True,
+    cli_exit_on_error=False,
+):
     my_required_field: str = Field(description='a top level required field')
 
 
@@ -896,13 +923,9 @@ os.environ['MY_REQUIRED_FIELD'] = 'hello from environment'
 try:
     sys.argv = ['example.py']
     Settings()
-except SystemExit as e:
+except SettingsError as e:
     print(e)
-    #> 2
-"""
-usage: example.py [-h] --my_required_field str
-example.py: error: the following arguments are required: --my_required_field
-"""
+    #> error parsing CLI: the following arguments are required: --my_required_field
 ```
 
 #### Change the None Type Parse String

pydantic_settings/__init__.py

@@ -11,6 +11,7 @@
     PydanticBaseSettingsSource,
     PyprojectTomlConfigSettingsSource,
     SecretsSettingsSource,
+    SettingsError,
     TomlConfigSettingsSource,
     YamlConfigSettingsSource,
 )
@@ -29,6 +30,7 @@
     'PydanticBaseSettingsSource',
     'SecretsSettingsSource',
     'SettingsConfigDict',
+    'SettingsError',
     'TomlConfigSettingsSource',
     'YamlConfigSettingsSource',
     'AzureKeyVaultSettingsSource',

pydantic_settings/main.py

@@ -38,6 +38,7 @@ class SettingsConfigDict(ConfigDict, total=False):
     cli_avoid_json: bool
     cli_enforce_required: bool
     cli_use_class_docs_for_groups: bool
+    cli_exit_on_error: bool
     cli_prefix: str
     secrets_dir: str | Path | None
     json_file: PathType | None
@@ -110,6 +111,8 @@ class BaseSettings(BaseModel):
         _cli_enforce_required: Enforce required fields at the CLI. Defaults to `False`.
         _cli_use_class_docs_for_groups: Use class docstrings in CLI group help text instead of field descriptions.
             Defaults to `False`.
+        _cli_exit_on_error: Determines whether or not the internal parser exits with error info when an error occurs.
+            Defaults to `True`.
         _cli_prefix: The root parser command line arguments prefix. Defaults to "".
         _secrets_dir: The secret files directory. Defaults to `None`.
     """
@@ -132,6 +135,7 @@ def __init__(
         _cli_avoid_json: bool | None = None,
         _cli_enforce_required: bool | None = None,
         _cli_use_class_docs_for_groups: bool | None = None,
+        _cli_exit_on_error: bool | None = None,
         _cli_prefix: str | None = None,
         _secrets_dir: str | Path | None = None,
         **values: Any,
@@ -156,6 +160,7 @@ def __init__(
                 _cli_avoid_json=_cli_avoid_json,
                 _cli_enforce_required=_cli_enforce_required,
                 _cli_use_class_docs_for_groups=_cli_use_class_docs_for_groups,
+                _cli_exit_on_error=_cli_exit_on_error,
                 _cli_prefix=_cli_prefix,
                 _secrets_dir=_secrets_dir,
             )
@@ -204,6 +209,7 @@ def _settings_build_values(
         _cli_avoid_json: bool | None = None,
         _cli_enforce_required: bool | None = None,
         _cli_use_class_docs_for_groups: bool | None = None,
+        _cli_exit_on_error: bool | None = None,
         _cli_prefix: str | None = None,
         _secrets_dir: str | Path | None = None,
     ) -> dict[str, Any]:
@@ -250,6 +256,9 @@ def _settings_build_values(
             if _cli_use_class_docs_for_groups is not None
             else self.model_config.get('cli_use_class_docs_for_groups')
         )
+        cli_exit_on_error = (
+            _cli_exit_on_error if _cli_exit_on_error is not None else self.model_config.get('cli_exit_on_error')
+        )
         cli_prefix = _cli_prefix if _cli_prefix is not None else self.model_config.get('cli_prefix')
 
         secrets_dir = _secrets_dir if _secrets_dir is not None else self.model_config.get('secrets_dir')
@@ -300,6 +309,7 @@ def _settings_build_values(
                         cli_avoid_json=cli_avoid_json,
                         cli_enforce_required=cli_enforce_required,
                         cli_use_class_docs_for_groups=cli_use_class_docs_for_groups,
+                        cli_exit_on_error=cli_exit_on_error,
                         cli_prefix=cli_prefix,
                         case_sensitive=case_sensitive,
                     )
@@ -346,6 +356,7 @@ def _settings_build_values(
         cli_avoid_json=False,
         cli_enforce_required=False,
         cli_use_class_docs_for_groups=False,
+        cli_exit_on_error=True,
         cli_prefix='',
         json_file=None,
         json_file_encoding=None,

pydantic_settings/sources.py

@@ -22,6 +22,7 @@
     Iterator,
     List,
     Mapping,
+    NoReturn,
     Optional,
     Sequence,
     Tuple,
@@ -110,6 +111,10 @@ def import_azure_key_vault() -> None:
 ENV_FILE_SENTINEL: DotenvType = Path('')
 
 
+class SettingsError(ValueError):
+    pass
+
+
 class _CliSubCommand:
     pass
 
@@ -119,7 +124,14 @@ class _CliPositionalArg:
 
 
 class _CliInternalArgParser(ArgumentParser):
-    pass
+    def __init__(self, cli_exit_on_error: bool = True, **kwargs: Any) -> None:
+        super().__init__(**kwargs)
+        self._cli_exit_on_error = cli_exit_on_error
+
+    def error(self, message: str) -> NoReturn:
+        if not self._cli_exit_on_error:
+            raise SettingsError(f'error parsing CLI: {message}')
+        super().error(message)
 
 
 T = TypeVar('T')
@@ -131,10 +143,6 @@ class EnvNoneType(str):
     pass
 
 
-class SettingsError(ValueError):
-    pass
-
-
 class PydanticBaseSettingsSource(ABC):
     """
     Abstract base class for settings sources, every settings source classes should inherit from it.
@@ -893,6 +901,8 @@ class CliSettingsSource(EnvSettingsSource, Generic[T]):
         cli_enforce_required: Enforce required fields at the CLI. Defaults to `False`.
         cli_use_class_docs_for_groups: Use class docstrings in CLI group help text instead of field descriptions.
             Defaults to `False`.
+        cli_exit_on_error: Determines whether or not the internal parser exits with error info when an error occurs.
+            Defaults to `True`.
         cli_prefix: Prefix for command line arguments added under the root parser. Defaults to "".
         case_sensitive: Whether CLI "--arg" names should be read with case-sensitivity. Defaults to `True`.
             Note: Case-insensitive matching is only supported on the internal root parser and does not apply to CLI
@@ -919,6 +929,7 @@ def __init__(
         cli_avoid_json: bool | None = None,
         cli_enforce_required: bool | None = None,
         cli_use_class_docs_for_groups: bool | None = None,
+        cli_exit_on_error: bool | None = None,
         cli_prefix: str | None = None,
         case_sensitive: bool | None = True,
         root_parser: Any = None,
@@ -953,6 +964,11 @@ def __init__(
             if cli_use_class_docs_for_groups is not None
             else settings_cls.model_config.get('cli_use_class_docs_for_groups', False)
         )
+        self.cli_exit_on_error = (
+            cli_exit_on_error
+            if cli_exit_on_error is not None
+            else settings_cls.model_config.get('cli_exit_on_error', True)
+        )
         self.cli_prefix = cli_prefix if cli_prefix is not None else settings_cls.model_config.get('cli_prefix', '')
         if self.cli_prefix:
             if cli_prefix.startswith('.') or cli_prefix.endswith('.') or not cli_prefix.replace('.', '').isidentifier():  # type: ignore
@@ -973,7 +989,9 @@ def __init__(
         )
 
         root_parser = (
-            _CliInternalArgParser(prog=self.cli_prog_name, description=settings_cls.__doc__)
+            _CliInternalArgParser(
+                cli_exit_on_error=self.cli_exit_on_error, prog=self.cli_prog_name, description=settings_cls.__doc__
+            )
             if root_parser is None
             else root_parser
         )