perf: build the StatusError message on first use

src/httpware/errors.py

@@ -23,6 +23,9 @@
 from httpware._internal.redaction import redact_url
 
 
+_EXCEPTION_ARGS: types.GetSetDescriptorType = BaseException.__dict__["args"]
+
+
 def _restore_client_error(cls: "type[ClientError]", args: tuple[Any, ...]) -> "ClientError":
     return cls.__new__(cls, *args)
 
@@ -71,7 +74,24 @@ class StatusError(ClientError):
 
     def __init__(self, response: httpx2.Response) -> None:
         self.response = response
-        super().__init__(self._summary())
+
+    @property
+    def args(self) -> tuple[Any, ...]:
+        """The one-element ``(message,)`` tuple, the message built on first access."""
+        args = _EXCEPTION_ARGS.__get__(self)
+        # BaseException.__new__ stored the constructor's (response,) here.
+        if len(args) == 1 and args[0] is vars(self).get("response"):
+            args = (self._summary(),)
+            _EXCEPTION_ARGS.__set__(self, args)
+        return args
+
+    @args.setter
+    def args(self, value: tuple[Any, ...]) -> None:
+        _EXCEPTION_ARGS.__set__(self, value)
+
+    def __str__(self) -> str:
+        args = self.args
+        return str(args[0]) if len(args) == 1 else super().__str__()
 
     def _summary(self) -> str:
         method = self.response.request.method

tests/test_errors.py

@@ -99,6 +99,29 @@ def test_status_error_summary_message_includes_status_method_url() -> None:
     assert str(exc) == "404 GET https://example.test/missing"
 
 
+def test_status_error_args_hold_the_summary_message() -> None:
+    exc = NotFoundError(_make_response(404, url="https://user:pass@example.test/x?token=s", method="GET"))
+    assert exc.args == ("404 GET https://example.test/x?token=REDACTED",)
+
+
+def test_status_error_builds_its_message_on_first_use(monkeypatch: pytest.MonkeyPatch) -> None:
+    redacted: list[str] = []
+    monkeypatch.setattr(httpware.errors, "redact_url", redacted.append)
+    NotFoundError(_make_response(404))
+    assert redacted == []
+
+
+@pytest.mark.parametrize(
+    ("args", "message"),
+    [(("custom",), "custom"), (("a", "b"), "('a', 'b')"), ((), "")],
+)
+def test_status_error_assigned_args_replace_the_message(args: tuple[str, ...], message: str) -> None:
+    exc = NotFoundError(_make_response(404))
+    exc.args = args
+    assert exc.args == args
+    assert str(exc) == message
+
+
 def test_status_error_strips_userinfo_in_summary_message() -> None:
     exc = NotFoundError(_make_response(404, url="https://user:pass@example.test/x"))
     assert "user" not in str(exc)