fix ExceptionPrettyPrinter custom formatter support

CHANGELOG.md

@@ -20,6 +20,10 @@ You can find our backwards-compatibility policy [here](https://github.com/hynek/
 - Support for Python 3.14 and Python 3.13.4.
   [#723](https://github.com/hynek/structlog/pull/723)
 
+### Fixed
+
+- `structlog.processors.ExceptionPrettyPrinter` now respects the *exception_formatter* arguments instead of always using the default formatter.
+
 
 ## [25.3.0](https://github.com/hynek/structlog/compare/25.2.0...25.3.0) - 2025-04-25
 

src/structlog/processors.py

@@ -626,16 +626,21 @@ def _figure_out_exc_info(v: Any) -> ExcInfo | None:
 
 class ExceptionPrettyPrinter:
     """
-    Pretty print exceptions and remove them from the ``event_dict``.
+    Pretty print exceptions rendered by *exception_formatter* and remove them
+    from the ``event_dict``.
 
     Args:
         file: Target file for output (default: ``sys.stdout``).
+        exception_formatter:
+            A callable that is used to format the exception from the
+            ``exc_info`` field into the ``exception`` field.
 
     This processor is mostly for development and testing so you can read
     exceptions properly formatted.
 
-    It behaves like `format_exc_info` except it removes the exception data from
-    the event dictionary after printing it.
+    It behaves like `format_exc_info`, except that it removes the exception data
+    from the event dictionary after printing it using the passed
+    *exception_formatter*, which defaults to Python's built-in traceback formatting.
 
     It's tolerant to having `format_exc_info` in front of itself in the
     processor chain but doesn't require it.  In other words, it handles both
@@ -645,13 +650,17 @@ class ExceptionPrettyPrinter:
 
     .. versionchanged:: 16.0.0
        Added support for passing exceptions as ``exc_info`` on Python 3.
+
+    .. versionchanged:: 25.4.0
+       Fixed *exception_formatter* so that it overrides the default if set.
     """
 
     def __init__(
         self,
         file: TextIO | None = None,
         exception_formatter: ExceptionTransformer = _format_exception,
     ) -> None:
+        self.format_exception = exception_formatter
         if file is not None:
             self._file = file
         else:
@@ -664,7 +673,7 @@ def __call__(
         if exc is None:
             exc_info = _figure_out_exc_info(event_dict.pop("exc_info", None))
             if exc_info:
-                exc = _format_exception(exc_info)
+                exc = self.format_exception(exc_info)
 
         if exc:
             print(exc, file=self._file)

tests/processors/test_processors.py

@@ -36,7 +36,7 @@
     format_exc_info,
 )
 from structlog.stdlib import ProcessorFormatter
-from structlog.typing import EventDict
+from structlog.typing import EventDict, ExcInfo
 
 from ..additional_frame import additional_frame
 
@@ -125,6 +125,26 @@ def test_prints_exception(self, sio):
         assert "test_prints_exception" in out
         assert "raise ValueError" in out
 
+    def test_uses_exception_formatter(self, sio):
+        """
+        If an `exception_formatter` is passed, use that to render the
+        exception rather than the default.
+        """
+
+        def formatter(exc_info: ExcInfo) -> str:
+            return f"error: {exc_info}"
+
+        epp = ExceptionPrettyPrinter(file=sio, exception_formatter=formatter)
+        try:
+            raise ValueError
+        except ValueError as e:
+            epp(None, None, {"exc_info": True})
+            formatted = formatter(e)
+
+        out = sio.getvalue()
+
+        assert formatted in out
+
     def test_removes_exception_after_printing(self, sio):
         """
         After pretty printing `exception` is removed from the event_dict.