Fix optional orjson/ujson import breaking fastapi.responses

Catches ImportError instead of ModuleNotFoundError to handle cases where the package exists but its C-extension fails to load.

fastapi/responses.py

@@ -26,13 +26,13 @@ class _OrjsonModule(Protocol):
 
 try:
     ujson = cast(_UjsonModule, importlib.import_module("ujson"))
-except ModuleNotFoundError:  # pragma: nocover
+except ImportError:  # pragma: nocover
     ujson = None  # type: ignore[assignment]
 
 
 try:
     orjson = cast(_OrjsonModule, importlib.import_module("orjson"))
-except ModuleNotFoundError:  # pragma: nocover
+except ImportError:  # pragma: nocover
     orjson = None  # type: ignore[assignment]
 
 

tests/test_responses_optional_imports.py

@@ -0,0 +1,26 @@
+import importlib
+import sys
+from typing import Any
+
+import pytest
+
+def test_optional_imports_broken_installation(monkeypatch: pytest.MonkeyPatch) -> None:
+    """
+    Test that an ImportError during the import of an optional JSON library
+    (like orjson or ujson) does not crash the entire fastapi.responses module.
+    """
+    real_import_module = importlib.import_module
+
+    def fake_import_module(name: str, package: str | None = None) -> Any:
+        if name in ("ujson", "orjson"):
+            raise ImportError(f"simulated binary/load failure for {name}")
+        return real_import_module(name, package)
+
+    monkeypatch.setattr(importlib, "import_module", fake_import_module)
+
+    # Force a reload to ensure the module initialization runs with our monkeypatch
+    if "fastapi.responses" in sys.modules:
+        del sys.modules["fastapi.responses"]
+
+    # This should not raise an ImportError
+    import fastapi.responses  # noqa: F401