Format ExceptionGroup gracefully on Python 3.11+

pysnooper/tracer.py

@@ -569,7 +569,7 @@ class Tracer:
                            format(**locals()))
 
         if event == 'exception':
-            exception = '\n'.join(traceback.format_exception_only(*arg[:2])).strip()
+            exception = utils.format_exception(*arg[:2])
             if self.max_variable_length:
                 exception = utils.truncate(exception, self.max_variable_length)
             self.write('{indent}{_FOREGROUND_RED}Exception:..... '

pysnooper/utils.py

@@ -3,6 +3,7 @@
 
 import abc
 import re
+import traceback
 
 import sys
 from .pycompat import ABC, string_types, collections_abc
@@ -87,6 +88,21 @@ def truncate(string, max_length):
         return u'{}...{}'.format(string[:left], string[-right:])
 
 
+def format_exception(exc_type, exc_value):
+    try:
+        is_group = isinstance(exc_value, BaseExceptionGroup)
+    except NameError:
+        is_group = False
+    if is_group:
+        sub_types = ', '.join(type(e).__name__ for e in exc_value.exceptions)
+        message = exc_value.args[0] if exc_value.args else ''
+        return u"{}: '{}' ({} sub-exceptions: {})".format(
+            exc_type.__name__, message,
+            len(exc_value.exceptions), sub_types,
+        )
+    return u'\n'.join(traceback.format_exception_only(exc_type, exc_value)).strip()
+
+
 def ensure_tuple(x):
     if isinstance(x, collections_abc.Iterable) and \
                                                not isinstance(x, string_types):

tests/test_pysnooper.py

@@ -1908,6 +1908,65 @@ def test_exception():
     )
 
 
+@pytest.mark.skipif(sys.version_info < (3, 11),
+                    reason='ExceptionGroup requires Python 3.11+')
+def test_exception_group():
+    string_io = io.StringIO()
+    @pysnooper.snoop(string_io, color=False)
+    def f():
+        raise ExceptionGroup('task errors', [ValueError('bad'), TypeError('wrong'), RuntimeError('fail')])
+
+    with pytest.raises(ExceptionGroup):
+        f()
+
+    output = string_io.getvalue()
+    assert_output(
+        output,
+        (
+            SourcePathEntry(),
+            CallEntry(),
+            LineEntry(),
+            ExceptionEntry(),
+            ExceptionValueEntry(
+                value_regex=r"ExceptionGroup: 'task errors' "
+                            r"\(3 sub-exceptions: ValueError, TypeError, "
+                            r"RuntimeError\)"
+            ),
+            CallEndedByExceptionEntry(),
+            ElapsedTimeEntry(),
+        )
+    )
+
+
+@pytest.mark.skipif(sys.version_info < (3, 11),
+                    reason='ExceptionGroup requires Python 3.11+')
+def test_nested_exception_group():
+    string_io = io.StringIO()
+    @pysnooper.snoop(string_io, color=False)
+    def f():
+        raise ExceptionGroup('outer', [ExceptionGroup('inner', [ValueError('deep')]), TypeError('shallow')])
+
+    with pytest.raises(ExceptionGroup):
+        f()
+
+    output = string_io.getvalue()
+    assert_output(
+        output,
+        (
+            SourcePathEntry(),
+            CallEntry(),
+            LineEntry(),
+            ExceptionEntry(),
+            ExceptionValueEntry(
+                value_regex=r"ExceptionGroup: 'outer' "
+                            r"\(2 sub-exceptions: ExceptionGroup, TypeError\)"
+            ),
+            CallEndedByExceptionEntry(),
+            ElapsedTimeEntry(),
+        )
+    )
+
+
 def test_exception_on_entry():
     @pysnooper.snoop(color=False)
     def f(x):