Implement B036 check for except BaseException without re-raising

README.rst

@@ -195,6 +195,8 @@ second usage. Save the result to a list if the result is needed multiple times.
 
 **B035**: Found dict comprehension with a static key - either a constant value or variable not from the comprehension expression. This will result in a dict with a single key that was repeatedly overwritten.
 
+**B036**: Found ``except BaseException:`` without re-raising (no ``raise`` in the top-level of the ``except`` block). This catches all kinds of things (Exception, SystemExit, KeyboardInterrupt...) and may prevent a program from exiting as expected.
+
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
 

bugbear.py

@@ -407,6 +407,12 @@ def visit_ExceptHandler(self, node):
             maybe_error = _check_redundant_excepthandlers(names, node)
             if maybe_error is not None:
                 self.errors.append(maybe_error)
+        if "BaseException" in names and not any(
+            isinstance(subnode, ast.Raise) and subnode.exc is None
+            for subnode in node.body
+        ):
+            self.errors.append(B036(node.lineno, node.col_offset))
+
         self.generic_visit(node)
 
     def visit_UAdd(self, node):
@@ -668,7 +674,7 @@ def check_for_b017(self, node):
                             and isinstance(item_context.func.value, ast.Name)
                             and item_context.func.value.id == "pytest"
                             and "match"
-                            not in [kwd.arg for kwd in item_context.keywords]
+                            not in (kwd.arg for kwd in item_context.keywords)
                         )
                     )
                 )
@@ -677,7 +683,7 @@ def check_for_b017(self, node):
                     and item_context.func.id == "raises"
                     and isinstance(item_context.func.ctx, ast.Load)
                     and "pytest.raises" in self._b005_imports
-                    and "match" not in [kwd.arg for kwd in item_context.keywords]
+                    and "match" not in (kwd.arg for kwd in item_context.keywords)
                 )
             )
             and len(item_context.args) == 1
@@ -1953,6 +1959,9 @@ def visit_Lambda(self, node):
 )
 B035 = Error(message="B035 Static key in dict comprehension {!r}.")
 
+B036 = Error(
+    message="B036 Don't except `BaseException` unless you plan to re-raise it."
+)
 
 # Warnings disabled by default.
 B901 = Error(

tests/b036.py

@@ -0,0 +1,35 @@
+
+try:
+    pass
+except BaseException:  # bad
+    print("aaa")
+    pass
+
+
+try:
+    pass
+except BaseException as ex:  # bad
+    print(ex)
+    pass
+
+
+try:
+    pass
+except ValueError:
+    raise
+except BaseException:  # bad
+    pass
+
+
+try:
+    pass
+except BaseException:  # ok - reraised
+    print("aaa")
+    raise
+
+
+try:
+    pass
+except BaseException as ex:  # bad - raised something else
+    print("aaa")
+    raise KeyError from ex

tests/test_bugbear.py

@@ -44,6 +44,7 @@
     B033,
     B034,
     B035,
+    B036,
     B901,
     B902,
     B903,
@@ -597,6 +598,18 @@ def test_b035(self):
         )
         self.assertEqual(errors, expected)
 
+    def test_b036(self) -> None:
+        filename = Path(__file__).absolute().parent / "b036.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = self.errors(
+            B036(4, 0),
+            B036(11, 0),
+            B036(20, 0),
+            B036(33, 0),
+        )
+        self.assertEqual(errors, expected)
+
     def test_b908(self):
         filename = Path(__file__).absolute().parent / "b908.py"
         bbc = BugBearChecker(filename=str(filename))