feat: support string login in build_config and add substitute_mapping_values (#63)

* feat: support string login in build_config and add substitute_mapping_values (#61, #62)

Extend build_config() to accept login: int | str | None. String logins
are coerced via the existing coerce_login() helper (empty/whitespace →
None, numeric strings → int, non-numeric → ValueError). When
allow_whole_dollar_env=True, ${ENV} and $ENV placeholders are expanded
before coercion, consistent with path/password/server behavior.

Add substitute_mapping_values(), a generic recursive helper that
substitutes environment placeholders in nested dicts/lists only for
caller-selected mapping keys. Non-selected fields (including literal
dollar signs) are preserved exactly. Supports blank_string_keys_as_none
to normalise empty strings to None after substitution. No application-
specific key names (e.g. mt5_login) are hard-coded in mt5cli.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Bump version to v0.9.5

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs+test: clarify substitute_mapping_values docstring and pin tuple behaviour

- Adds sentence noting list-element strings are never substituted (only
  immediate dict values are), addressing reviewer finding #1.
- Rewrites Returns section to accurately describe scalar pass-through
  behaviour, addressing reviewer finding #2.
- Adds recursion-depth caveat to the generic-utility docstring,
  addressing reviewer finding #4.
- Adds test_tuple_container_not_traversed to pin the existing silent
  tuple-exclusion contract, addressing reviewer finding #3.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* docs: update public contract and README for build_config login coercion and substitute_mapping_values

- Expands build_config row to document login: int | str | None,
  numeric-string coercion, blank-string handling, and env placeholder
  expansion when allow_whole_dollar_env=True.
- Adds substitute_mapping_values to the stable SDK table with a note
  that key names are never hard-coded in mt5cli.
- Extends allow_whole_dollar_env paragraph to list substitute_mapping_values.
- README: adds build_config env-placeholder example and imports to the
  trading lifecycle snippet.
- README: extends credential-resolution bullet with a substitute_mapping_values
  usage example using generic key names.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: agent <agent@localhost>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -92,16 +92,21 @@ Schema contracts live in `mt5cli.schemas` (`DataKind`, `validate_schema`, `norma
 Trading applications can depend on `mt5cli` imports only; terminal path,
 credentials, server, and timeout are forwarded to `pdmt5.Mt5Config`, numeric
 login strings are coerced to integers, and empty login strings are treated as
-unset.
+unset. Pass `allow_whole_dollar_env=True` to expand `${ENV_VAR}` and bare
+`$ENV_NAME` placeholders in connection string parameters before coercion.
 
 ```python
 from mt5cli import (
+    build_config,
     calculate_spread_ratio,
     create_trading_client,
     get_account_snapshot,
     mt5_trading_session,
 )
 
+# Login from environment — numeric string is coerced to int automatically
+config = build_config(login="$MT5_LOGIN", allow_whole_dollar_env=True)
+
 with mt5_trading_session(
     path=r"C:\Program Files\MetaTrader 5\terminal64.exe",
     login="12345",
@@ -248,7 +253,7 @@ rates = collect_latest_closed_rates_by_granularity(
 eurusd_m1 = rates["EURUSD", "M1"]  # closed bars only
 ```
 
-- **Credential resolution**: use `resolve_account_spec()` / `resolve_account_specs()` to merge explicit override values over `AccountSpec` fields and expand `${ENV_VAR}` placeholders (via `substitute_env_placeholders()`), raising `ValueError` for missing variables. This keeps secrets out of plan/config files without coupling to any strategy code.
+- **Credential resolution**: use `resolve_account_spec()` / `resolve_account_specs()` to merge explicit override values over `AccountSpec` fields and expand `${ENV_VAR}` placeholders (via `substitute_env_placeholders()`), raising `ValueError` for missing variables. This keeps secrets out of plan/config files without coupling to any strategy code. For config dicts or nested structures loaded from YAML/TOML, use `substitute_mapping_values(data, keys={"login", "password"})` to expand placeholders only for caller-specified keys — key names are never hard-coded in mt5cli.
 - **Throttled history updates**: use `ThrottledHistoryUpdater` to wrap `update_history()` with a minimum `interval_seconds` between successful runs (monotonic clock). Call `should_update()` / `update(client, symbols)` from an application loop; errors propagate by default, or pass `suppress_errors=True` to swallow recoverable `Mt5*Error`, `sqlite3.Error`, `ValueError`, `OSError`, and MT5 client capability errors for history API methods without advancing the throttle (other `AttributeError` / `TypeError` values always propagate). Pass `update_backend` to inject a custom history update callable (same keyword arguments as `update_history`) instead of monkey-patching `mt5cli.sdk.update_history`.
 - **Trading session helpers**: use `mt5_trading_session()` for a trading-capable `pdmt5.Mt5TradingClient` that initializes/logs in via `Mt5Config.path` and always shuts down safely. Pair with `detect_position_side()`, `calculate_margin_and_volume()`, and `determine_order_limits()` for generic position and sizing utilities. Keep read-only collection on `mt5_session()` / `MT5Client`.
 - **Granularity-keyed rate loading**: `load_rate_series_by_granularity()` builds targets with `build_rate_targets()`, loads them with `load_rate_series_from_sqlite()`, and returns a mapping keyed by `(symbol | None, granularity_name)` such as `("EURUSD", "M1")` to reduce downstream boilerplate.

docs/api/public-contract.md

@@ -28,23 +28,25 @@ These names are exported from `mt5cli` and covered by the contract in
 
 ### Session lifecycle and configuration
 
-| Symbol                                          | Role                                                                                                       |
+| Symbol                                          | Role                                                                                                                                                                                                                                                                              |
-| ----------------------------------------------- | ---------------------------------------------------------------------------------------------------------- |
+| ----------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
-| `MT5Client`                                     | Read-only data client with optional `order_check` / `order_send`                                           |
+| `MT5Client`                                     | Read-only data client with optional `order_check` / `order_send`                                                                                                                                                                                                                  |
-| `build_config`                                  | Build `pdmt5.Mt5Config` from connection fields                                                             |
+| `build_config`                                  | Build `pdmt5.Mt5Config` from connection fields; `login` accepts `int \| str \| None` — numeric strings are coerced to `int`, blank strings are treated as unset, and `${ENV_VAR}` / `$ENV_NAME` placeholders in string parameters are expanded when `allow_whole_dollar_env=True` |
-| `mt5_session`                                   | Context manager: initialize, login, yield client, shutdown                                                 |
+| `mt5_session`                                   | Context manager: initialize, login, yield client, shutdown                                                                                                                                                                                                                        |
-| `create_trading_client`, `mt5_trading_session`  | Trading-capable `pdmt5.Mt5TradingClient` lifecycle                                                         |
+| `create_trading_client`, `mt5_trading_session`  | Trading-capable `pdmt5.Mt5TradingClient` lifecycle                                                                                                                                                                                                                                |
-| `AccountSpec`                                   | Generic account group: symbols plus optional credentials                                                   |
+| `AccountSpec`                                   | Generic account group: symbols plus optional credentials                                                                                                                                                                                                                          |
-| `resolve_account_spec`, `resolve_account_specs` | Merge overrides and expand `${ENV_VAR}` placeholders; opt-in `allow_whole_dollar_env` for bare `$NAME`     |
+| `resolve_account_spec`, `resolve_account_specs` | Merge overrides and expand `${ENV_VAR}` placeholders; opt-in `allow_whole_dollar_env` for bare `$NAME`                                                                                                                                                                            |
-| `substitute_env_placeholders`                   | Replace `${NAME}` substrings from the environment; opt-in `allow_whole_dollar_env` for whole-value `$NAME` |
+| `substitute_env_placeholders`                   | Replace `${NAME}` substrings from the environment; opt-in `allow_whole_dollar_env` for whole-value `$NAME`                                                                                                                                                                        |
+| `substitute_mapping_values`                     | Recursively traverse a dict/list/scalar structure and substitute `${ENV_VAR}` placeholders for caller-selected mapping keys only; optionally normalise blank strings to `None` for a separate caller-selected key set; does not hard-code any application-specific key names      |
 
 Credential resolution is generic: any environment variable name may appear inside
 `${...}`. mt5cli does not hard-code application-specific keys such as
 `mt5_login` or `mt5_exe`.
 
 Pass `allow_whole_dollar_env=True` to `substitute_env_placeholders()`,
-`resolve_account_spec()`, `resolve_account_specs()`, and `build_config()` to
+`substitute_mapping_values()`, `resolve_account_spec()`, `resolve_account_specs()`,
-additionally expand strings whose entire value is a bare `$ENV_NAME` identifier.
+and `build_config()` to additionally expand strings whose entire value is a bare
+`$ENV_NAME` identifier.
 Partial strings such as `"plan$pass"`, `"abc$ENV"`, or `"$ENV-suffix"` are
 **never** expanded — only an exact `$IDENTIFIER` whole-string match qualifies.
 Default is `False` to preserve backward compatibility.

mt5cli/__init__.py

@@ -92,6 +92,7 @@ from .sdk import (
     resolve_account_spec,
     resolve_account_specs,
     substitute_env_placeholders,
+    substitute_mapping_values,
     symbol_info,
     symbol_info_tick,
     symbols,
@@ -283,6 +284,7 @@ __all__ = [
     "resolve_rate_view_names",
     "schema_columns",
     "substitute_env_placeholders",
+    "substitute_mapping_values",
     "symbol_info",
     "symbol_info_tick",
     "symbols",

mt5cli/contract.py

@@ -77,6 +77,7 @@ STABLE_SDK_EXPORTS: frozenset[str] = frozenset({
     "resolve_rate_view_name",
     "resolve_rate_view_names",
     "substitute_env_placeholders",
+    "substitute_mapping_values",
     "update_history",
     "update_history_with_config",
     "update_sltp_for_open_positions",

mt5cli/sdk.py

@@ -40,7 +40,7 @@ from .utils import (
 from .utils import coerce_login as _coerce_login
 
 if TYPE_CHECKING:
-    from collections.abc import Callable, Iterator, Sequence
+    from collections.abc import Callable, Collection, Iterator, Sequence
 
     UpdateHistoryBackend = Callable[..., None]
 
@@ -142,6 +142,7 @@ __all__ = [
     "resolve_account_spec",
     "resolve_account_specs",
     "substitute_env_placeholders",
+    "substitute_mapping_values",
     "symbol_info",
     "symbol_info_tick",
     "symbols",
@@ -305,7 +306,7 @@ def _fetch_minimum_margins(client: Mt5DataClient, symbol: str) -> pd.DataFrame:
 def build_config(
     *,
     path: str | None = None,
-    login: int | None = None,
+    login: int | str | None = None,
     password: str | None = None,
     server: str | None = None,
     timeout: int | None = None,
@@ -315,14 +316,19 @@ def build_config(
 
     Args:
         path: Optional terminal executable path.
-        login: Optional trading account login.
+        login: Optional trading account login. Integers are preserved. String
+            values are coerced: empty or whitespace-only strings become
+            ``None``; numeric strings such as ``"12345"`` are converted to
+            ``int``; non-numeric strings raise ``ValueError``. When
+            ``allow_whole_dollar_env=True``, ``$ENV_NAME`` and
+            ``${ENV_NAME}`` placeholders are expanded before coercion.
         password: Optional trading account password.
         server: Optional trading server name.
         timeout: Optional connection timeout in milliseconds.
         allow_whole_dollar_env: When ``True``, string parameters that are
             exactly ``$ENV_NAME`` are expanded from the environment. Applies
-            to ``path``, ``password``, and ``server``. Default ``False``
+            to ``path``, ``login``, ``password``, and ``server``. Default
-            preserves existing behavior.
+            ``False`` preserves existing behavior.
 
     Returns:
         Configured ``Mt5Config`` instance.
@@ -330,6 +336,8 @@ def build_config(
     if allow_whole_dollar_env:
         if path is not None:
             path = substitute_env_placeholders(path, allow_whole_dollar_env=True)
+        if isinstance(login, str):
+            login = substitute_env_placeholders(login, allow_whole_dollar_env=True)
         if password is not None:
             password = substitute_env_placeholders(
                 password, allow_whole_dollar_env=True
@@ -338,7 +346,7 @@ def build_config(
             server = substitute_env_placeholders(server, allow_whole_dollar_env=True)
     return Mt5Config(
         path=path,
-        login=login,
+        login=_coerce_login(login),
         password=password,
         server=server,
         timeout=timeout,
@@ -1442,6 +1450,75 @@ def substitute_env_placeholders(
     return "".join(parts)
 
 
+def substitute_mapping_values(
+    data: object,
+    *,
+    keys: Collection[str],
+    allow_whole_dollar_env: bool = False,
+    blank_string_keys_as_none: Collection[str] = (),
+) -> object:
+    """Recursively substitute environment placeholders for selected mapping keys.
+
+    Traverses nested dicts and lists, expanding ``${ENV_VAR}`` (and
+    ``$ENV_NAME`` when ``allow_whole_dollar_env=True``) in string values
+    whose immediate parent dict key is in ``keys``.  Fields whose key is
+    not in ``keys`` are preserved exactly, including literal dollar signs.
+    Strings that are direct elements of a list are never substituted;
+    substitution only applies to strings that are immediate dict values.
+
+    This is a generic downstream config utility.  Key names such as
+    ``mt5_login`` or ``mt5_password`` must be supplied by the caller;
+    mt5cli does not hard-code any application-specific key names.
+    Callers are responsible for ensuring ``data`` has bounded nesting depth;
+    deeply nested or self-referential structures will hit Python's recursion
+    limit.
+
+    Args:
+        data: Arbitrarily nested dict/list/scalar value to process.
+        keys: Mapping keys whose string values receive placeholder
+            substitution.
+        allow_whole_dollar_env: When ``True``, a string that is exactly
+            ``$ENV_NAME`` (whole value) is also expanded from the
+            environment in addition to ``${ENV_NAME}`` placeholders.
+            Default ``False`` expands ``${ENV_NAME}`` only.
+        blank_string_keys_as_none: Mapping keys for which blank strings
+            (after any substitution) are normalised to ``None``.  A key
+            may appear in ``blank_string_keys_as_none`` without also
+            appearing in ``keys``.
+
+    Returns:
+        The processed value.  Dicts and lists are rebuilt into new
+        containers with selected string values substituted and
+        blank-normalised.  Scalar inputs (non-dict, non-list) are
+        returned as-is.
+    """
+    keys_set: frozenset[str] = frozenset(keys)
+    blank_keys_set: frozenset[str] = frozenset(blank_string_keys_as_none)
+
+    def _visit(node: object, current_key: str | None) -> object:
+        if isinstance(node, dict):
+            typed = cast("dict[object, object]", node)
+            return {
+                k: _visit(v, k if isinstance(k, str) else None)
+                for k, v in typed.items()
+            }
+        if isinstance(node, list):
+            typed_list = cast("list[object]", node)
+            return [_visit(item, None) for item in typed_list]
+        if not isinstance(node, str):
+            return node
+        text = node
+        if current_key in keys_set:
+            text = substitute_env_placeholders(
+                node, allow_whole_dollar_env=allow_whole_dollar_env
+            )
+        if current_key in blank_keys_set and not text.strip():
+            return None
+        return text
+
+    return _visit(data, None)
+
+
 def _resolve_field(
     override: str | None,
     account_value: str | None,

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "mt5cli"
-version = "0.9.4"
+version = "0.9.5"
 description = "Generic MT5 data and execution infrastructure for Python applications"
 authors = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]
 maintainers = [{name = "dceoy", email = "dceoy@users.noreply.github.com"}]

tests/test_sdk.py

@@ -54,6 +54,7 @@ from mt5cli.sdk import (
     resolve_account_spec,
     resolve_account_specs,
     substitute_env_placeholders,
+    substitute_mapping_values,
     symbol_info,
     symbol_info_tick,
     symbols,
@@ -2436,3 +2437,263 @@ class TestThrottledHistoryUpdater:
             updater.update(MagicMock(), ["EURUSD"])
 
         assert updater.last_update_monotonic is None
+
+
+class TestBuildConfigStringLogin:
+    """Tests for build_config() string login coercion (issue #61)."""
+
+    @pytest.mark.parametrize(
+        ("login", "expected"),
+        [
+            (None, None),
+            (12345, 12345),
+            ("12345", 12345),
+            (" 12345 ", 12345),
+            ("", None),
+            ("   ", None),
+        ],
+    )
+    def test_coerces_login_from_string(
+        self,
+        login: int | str | None,
+        expected: int | None,
+    ) -> None:
+        """Test build_config coerces string login to int or None."""
+        config = build_config(login=login)
+        assert config.login == expected
+
+    def test_rejects_non_numeric_string_login(self) -> None:
+        """Test build_config raises ValueError for non-numeric string login."""
+        with pytest.raises(ValueError, match="invalid literal"):
+            build_config(login="abc")
+
+    def test_expands_dollar_brace_login_with_opt_in(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test build_config expands ${MT5_LOGIN} and coerces with opt-in."""
+        monkeypatch.setenv("MT5_LOGIN", "12345")
+        config = build_config(login="${MT5_LOGIN}", allow_whole_dollar_env=True)
+        assert config.login == 12345
+
+    def test_expands_whole_dollar_login_with_opt_in(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test build_config expands $MT5_LOGIN and coerces with opt-in."""
+        monkeypatch.setenv("MT5_LOGIN", "99999")
+        config = build_config(login="$MT5_LOGIN", allow_whole_dollar_env=True)
+        assert config.login == 99999
+
+    def test_missing_env_variable_raises(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test build_config raises ValueError when referenced env var is not set."""
+        monkeypatch.delenv("MT5_LOGIN", raising=False)
+        with pytest.raises(ValueError, match="'MT5_LOGIN' is not set"):
+            build_config(login="${MT5_LOGIN}", allow_whole_dollar_env=True)
+
+    def test_env_expands_to_blank_becomes_none(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test build_config coerces blank env-expanded login to None."""
+        monkeypatch.setenv("MT5_LOGIN", "")
+        config = build_config(login="${MT5_LOGIN}", allow_whole_dollar_env=True)
+        assert config.login is None
+
+    def test_dollar_brace_login_not_expanded_without_opt_in(self) -> None:
+        """Test ${MT5_LOGIN} is not expanded when allow_whole_dollar_env=False."""
+        with pytest.raises(ValueError, match="invalid literal"):
+            build_config(login="${MT5_LOGIN}")
+
+    def test_integer_login_preserved_backward_compat(self) -> None:
+        """Test existing int login callers remain backward-compatible."""
+        config = build_config(login=54321)
+        assert config.login == 54321
+
+    def test_none_login_preserved_backward_compat(self) -> None:
+        """Test existing None login callers remain backward-compatible."""
+        config = build_config(login=None)
+        assert config.login is None
+
+
+class TestSubstituteMappingValues:
+    """Tests for substitute_mapping_values() (issue #62)."""
+
+    def test_substitutes_selected_keys_in_flat_dict(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test selected keys are substituted in a flat mapping."""
+        monkeypatch.setenv("MT5_LOGIN", "12345")
+        data: dict[str, object] = {
+            "mt5_login": "${MT5_LOGIN}",
+            "strategy_name": "${MT5_LOGIN}",
+        }
+        result = substitute_mapping_values(data, keys={"mt5_login"})
+        assert result == {"mt5_login": "12345", "strategy_name": "${MT5_LOGIN}"}
+
+    def test_preserves_non_selected_literal_dollar_signs(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test literal dollar signs in non-selected fields are preserved exactly."""
+        monkeypatch.setenv("MT5_PASSWORD", "secret")
+        data: dict[str, object] = {
+            "mt5_password": "${MT5_PASSWORD}",
+            "notes": "$NOT_EXPANDED",
+        }
+        result = substitute_mapping_values(data, keys={"mt5_password"})
+        assert result == {"mt5_password": "secret", "notes": "$NOT_EXPANDED"}
+
+    def test_nested_dict_traversal_substitutes_selected_keys(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test selected keys inside nested dicts are substituted."""
+        monkeypatch.setenv("MT5_SERVER", "Broker-Demo")
+        data: dict[str, object] = {
+            "outer": {
+                "mt5_server": "${MT5_SERVER}",
+                "other": "${MT5_SERVER}",
+            }
+        }
+        result = substitute_mapping_values(data, keys={"mt5_server"})
+        assert result == {
+            "outer": {"mt5_server": "Broker-Demo", "other": "${MT5_SERVER}"}
+        }
+
+    def test_nested_list_traversal_substitutes_selected_keys(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test selected keys inside list elements are substituted."""
+        monkeypatch.setenv("MT5_LOGIN", "42")
+        data: dict[str, object] = {
+            "accounts": [
+                {"mt5_login": "${MT5_LOGIN}", "name": "${MT5_LOGIN}"},
+                {"mt5_login": "${MT5_LOGIN}", "name": "fixed"},
+            ]
+        }
+        result = substitute_mapping_values(data, keys={"mt5_login"})
+        assert result == {
+            "accounts": [
+                {"mt5_login": "42", "name": "${MT5_LOGIN}"},
+                {"mt5_login": "42", "name": "fixed"},
+            ]
+        }
+
+    def test_whole_dollar_expanded_with_opt_in(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test $ENV_NAME is expanded when allow_whole_dollar_env=True."""
+        monkeypatch.setenv("MT5_PASSWORD", "secret")
+        data: dict[str, object] = {"mt5_password": "$MT5_PASSWORD"}
+        result = substitute_mapping_values(
+            data,
+            keys={"mt5_password"},
+            allow_whole_dollar_env=True,
+        )
+        assert result == {"mt5_password": "secret"}
+
+    def test_whole_dollar_not_expanded_by_default(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test $ENV_NAME in a selected key is preserved when opt-in is False."""
+        monkeypatch.setenv("MT5_PASSWORD", "secret")
+        data: dict[str, object] = {"mt5_password": "$MT5_PASSWORD"}
+        result = substitute_mapping_values(data, keys={"mt5_password"})
+        assert result == {"mt5_password": "$MT5_PASSWORD"}
+
+    def test_blank_string_becomes_none_for_blank_keys(self) -> None:
+        """Test blank strings are normalised to None for blank_string_keys_as_none."""
+        data: dict[str, object] = {
+            "mt5_login": "",
+            "mt5_password": "  ",
+            "other": "",
+        }
+        result = substitute_mapping_values(
+            data,
+            keys=set(),
+            blank_string_keys_as_none={"mt5_login", "mt5_password"},
+        )
+        assert result == {"mt5_login": None, "mt5_password": None, "other": ""}
+
+    def test_env_expanded_blank_becomes_none(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test env-expanded blank string is normalised to None."""
+        monkeypatch.setenv("MT5_LOGIN", "")
+        data: dict[str, object] = {"mt5_login": "${MT5_LOGIN}"}
+        result = substitute_mapping_values(
+            data,
+            keys={"mt5_login"},
+            blank_string_keys_as_none={"mt5_login"},
+        )
+        assert result == {"mt5_login": None}
+
+    def test_missing_env_variable_raises_for_selected_key(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test missing env var for a selected key raises ValueError."""
+        monkeypatch.delenv("MT5_MISSING", raising=False)
+        data: dict[str, object] = {"mt5_login": "${MT5_MISSING}"}
+        with pytest.raises(ValueError, match="'MT5_MISSING' is not set"):
+            substitute_mapping_values(data, keys={"mt5_login"})
+
+    def test_non_string_values_preserved(self) -> None:
+        """Test non-string values under selected or non-selected keys are preserved."""
+        data: dict[str, object] = {
+            "mt5_login": 12345,
+            "timeout": 5000,
+            "enabled": True,
+            "ratio": 1.5,
+            "nothing": None,
+        }
+        result = substitute_mapping_values(
+            data, keys={"mt5_login", "timeout", "enabled", "ratio", "nothing"}
+        )
+        assert result == data
+
+    def test_caller_supplied_key_set_substitutes_correctly(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test helper works with any caller-supplied key set."""
+        monkeypatch.setenv("APP_LOGIN", "77777")
+        monkeypatch.setenv("APP_PASSWORD", "p4ss")
+        data: dict[str, object] = {
+            "app_login": "${APP_LOGIN}",
+            "app_password": "${APP_PASSWORD}",
+            "unrelated": "${APP_LOGIN}",
+        }
+        credential_keys = {"app_login", "app_password"}
+        result = substitute_mapping_values(data, keys=credential_keys)
+        assert result == {
+            "app_login": "77777",
+            "app_password": "p4ss",
+            "unrelated": "${APP_LOGIN}",
+        }
+
+    def test_scalar_data_returned_unchanged(self) -> None:
+        """Test a scalar (non-dict, non-list) value is returned as-is."""
+        assert substitute_mapping_values("hello", keys={"x"}) == "hello"
+        assert substitute_mapping_values(42, keys={"x"}) == 42
+        assert substitute_mapping_values(None, keys={"x"}) is None
+
+    def test_tuple_container_not_traversed(
+        self,
+        monkeypatch: pytest.MonkeyPatch,
+    ) -> None:
+        """Test tuple containers are returned as-is without traversal."""
+        monkeypatch.setenv("MT5_LOGIN", "42")
+        data: dict[str, object] = {"accounts": ({"mt5_login": "${MT5_LOGIN}"},)}
+        result = substitute_mapping_values(data, keys={"mt5_login"})
+        # tuple is returned as-is; inner dict is NOT visited
+        assert result == {"accounts": ({"mt5_login": "${MT5_LOGIN}"},)}

uv.lock

@@ -487,7 +487,7 @@ wheels = [
 
 [[package]]
 name = "mt5cli"
-version = "0.9.4"
+version = "0.9.5"
 source = { editable = "." }
 dependencies = [
     { name = "click" },