fix: handle non-JSON-serializable objects in TogetherException repr

Add `default=str` to `json.dumps()` in `TogetherException.__repr__()` so
that non-serializable objects (like aiohttp's CIMultiDictProxy headers)
fall back to their string representation instead of raising TypeError.

Fixes #108

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

Author: MaxwellCalkin

src/together/error.py

@@ -44,7 +44,8 @@ def __repr__(self) -> str:
                 "status": self.http_status,
                 "request_id": self.request_id,
                 "headers": self.headers,
-            }
+            },
+            default=str,
         )
         return "%s(%r)" % (self.__class__.__name__, repr_message)
 

tests/unit/test_exception_repr.py

@@ -0,0 +1,109 @@
+"""Tests for TogetherException.__repr__ with non-JSON-serializable objects.
+
+Regression tests for https://github.com/togethercomputer/together-python/issues/108
+where repr() on a TogetherException crashed with TypeError when headers
+contained non-serializable objects like aiohttp's CIMultiDictProxy.
+"""
+
+from __future__ import annotations
+
+import json
+from typing import Any, Iterator
+
+import pytest
+
+from together.error import (
+    APIConnectionError,
+    APIError,
+    AuthenticationError,
+    JSONError,
+    RateLimitError,
+    ResponseError,
+    Timeout,
+    TogetherException,
+)
+
+
+class FakeCIMultiDictProxy:
+    """Mimics aiohttp's CIMultiDictProxy, which is not JSON-serializable."""
+
+    def __init__(self, data: dict[str, str]) -> None:
+        self._data = data
+
+    def __iter__(self) -> Iterator[str]:
+        return iter(self._data)
+
+    def __len__(self) -> int:
+        return len(self._data)
+
+    def __getitem__(self, key: str) -> str:
+        return self._data[key]
+
+    def __repr__(self) -> str:
+        return f"<CIMultiDictProxy({self._data!r})>"
+
+
+class TestExceptionReprNonSerializable:
+    """repr() must never crash, even with non-JSON-serializable attributes."""
+
+    def test_repr_with_non_serializable_headers(self) -> None:
+        """Core bug from issue #108: CIMultiDictProxy headers crash repr()."""
+        headers = FakeCIMultiDictProxy({"Content-Type": "application/json"})
+        exc = TogetherException(
+            message="server error",
+            headers=headers,  # type: ignore[arg-type]
+            http_status=500,
+        )
+        # Before fix: TypeError: Object of type FakeCIMultiDictProxy is not
+        #             JSON serializable
+        result = repr(exc)
+        assert "TogetherException" in result
+        assert "server error" in result
+
+    def test_repr_with_dict_headers(self) -> None:
+        """Normal dict headers must still work (regression check)."""
+        exc = TogetherException(
+            message="bad request",
+            headers={"X-Request-Id": "abc-123"},
+            http_status=400,
+            request_id="req-1",
+        )
+        result = repr(exc)
+        parsed = json.loads(result.split("(", 1)[1].rsplit(")", 1)[0].strip("'\""))
+        assert parsed["status"] == 400
+        assert parsed["request_id"] == "req-1"
+
+    def test_repr_with_none_headers(self) -> None:
+        """Default None headers (stored as {}) must work."""
+        exc = TogetherException(message="oops")
+        result = repr(exc)
+        assert "TogetherException" in result
+
+    def test_repr_with_string_headers(self) -> None:
+        """String headers must work."""
+        exc = TogetherException(message="err", headers="raw-header")
+        result = repr(exc)
+        assert "raw-header" in result
+
+    @pytest.mark.parametrize(
+        "exc_class",
+        [
+            AuthenticationError,
+            ResponseError,
+            JSONError,
+            RateLimitError,
+            Timeout,
+            APIConnectionError,
+            APIError,
+        ],
+    )
+    def test_subclasses_inherit_fix(self, exc_class: type) -> None:
+        """All subclasses inherit the safe repr via TogetherException."""
+        headers = FakeCIMultiDictProxy({"X-Rate-Limit": "100"})
+        exc = exc_class(
+            message="subclass test",
+            headers=headers,  # type: ignore[arg-type]
+            http_status=429,
+        )
+        result = repr(exc)
+        assert exc_class.__name__ in result