Remove binding of captured exceptions when not used to reduce the chances of creating cycles (GH-17246)

Capturing exceptions into names can lead to reference cycles though the __traceback__ attribute of the exceptions in some obscure cases that have been reported previously and fixed individually. As these variables are not used anyway, we can remove the binding to reduce the chances of creating reference cycles.

See for example GH-13135

Lib/asynchat.py

@@ -117,7 +117,7 @@ class async_chat(asyncore.dispatcher):
             data = self.recv(self.ac_in_buffer_size)
         except BlockingIOError:
             return
-        except OSError as why:
+        except OSError:
             self.handle_error()
             return
 

Lib/asyncio/proactor_events.py

@@ -711,7 +711,7 @@ class BaseProactorEventLoop(base_events.BaseEventLoop):
             raise exceptions.SendfileNotAvailableError("not a regular file")
         try:
             fsize = os.fstat(fileno).st_size
-        except OSError as err:
+        except OSError:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         blocksize = count if count else fsize
         if not blocksize:

Lib/asyncio/unix_events.py

@@ -330,7 +330,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
     async def _sock_sendfile_native(self, sock, file, offset, count):
         try:
             os.sendfile
-        except AttributeError as exc:
+        except AttributeError:
             raise exceptions.SendfileNotAvailableError(
                 "os.sendfile() is not available")
         try:
@@ -339,7 +339,7 @@ class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
             raise exceptions.SendfileNotAvailableError("not a regular file")
         try:
             fsize = os.fstat(fileno).st_size
-        except OSError as err:
+        except OSError:
             raise exceptions.SendfileNotAvailableError("not a regular file")
         blocksize = count if count else fsize
         if not blocksize:

Lib/codeop.py

@@ -80,7 +80,7 @@ def _maybe_compile(compiler, source, filename, symbol):
 
     try:
         code = compiler(source, filename, symbol)
-    except SyntaxError as err:
+    except SyntaxError:
         pass
 
     try:

Lib/ctypes/util.py

@@ -302,7 +302,7 @@ elif os.name == "posix":
                 res = re.search(expr, os.fsdecode(out))
                 if res:
                     result = res.group(0)
-            except Exception as e:
+            except Exception:
                 pass  # result will be None
             return result
 

Lib/enum.py

@@ -420,7 +420,7 @@ class EnumMeta(type):
         if module is None:
             try:
                 module = sys._getframe(2).f_globals['__name__']
-            except (AttributeError, ValueError, KeyError) as exc:
+            except (AttributeError, ValueError, KeyError):
                 pass
         if module is None:
             _make_class_unpicklable(enum_class)

Lib/filecmp.py

@@ -156,12 +156,12 @@ class dircmp:
             ok = 1
             try:
                 a_stat = os.stat(a_path)
-            except OSError as why:
+            except OSError:
                 # print('Can\'t stat', a_path, ':', why.args[1])
                 ok = 0
             try:
                 b_stat = os.stat(b_path)
-            except OSError as why:
+            except OSError:
                 # print('Can\'t stat', b_path, ':', why.args[1])
                 ok = 0
 

Lib/getpass.py

@@ -52,7 +52,7 @@ def unix_getpass(prompt='Password: ', stream=None):
             stack.enter_context(input)
             if not stream:
                 stream = input
-        except OSError as e:
+        except OSError:
             # If that fails, see if stdin can be controlled.
             stack.close()
             try:

Lib/importlib/abc.py

@@ -10,7 +10,7 @@ except ImportError as exc:
     _frozen_importlib = None
 try:
     import _frozen_importlib_external
-except ImportError as exc:
+except ImportError:
     _frozen_importlib_external = _bootstrap_external
 import abc
 import warnings

Lib/lib2to3/main.py

@@ -90,11 +90,11 @@ class StdoutRefactoringTool(refactor.MultiprocessRefactoringTool):
             if os.path.lexists(backup):
                 try:
                     os.remove(backup)
-                except OSError as err:
+                except OSError:
                     self.log_message("Can't remove backup %s", backup)
             try:
                 os.rename(filename, backup)
-            except OSError as err:
+            except OSError:
                 self.log_message("Can't rename %s to %s", filename, backup)
         # Actually write the new file
         write = super(StdoutRefactoringTool, self).write_file

Lib/msilib/__init__.py

@@ -116,7 +116,7 @@ def add_data(db, table, values):
                 raise TypeError("Unsupported type %s" % field.__class__.__name__)
         try:
             v.Modify(MSIMODIFY_INSERT, r)
-        except Exception as e:
+        except Exception:
             raise MSIError("Could not insert "+repr(values)+" into "+table)
 
         r.ClearData()

Lib/multiprocessing/managers.py

@@ -248,7 +248,7 @@ class Server(object):
                     try:
                         obj, exposed, gettypeid = \
                             self.id_to_local_proxy_obj[ident]
-                    except KeyError as second_ke:
+                    except KeyError:
                         raise ke
 
                 if methodname not in exposed:
@@ -296,7 +296,7 @@ class Server(object):
             try:
                 try:
                     send(msg)
-                except Exception as e:
+                except Exception:
                     send(('#UNSERIALIZABLE', format_exc()))
             except Exception as e:
                 util.info('exception in thread serving %r',

Lib/multiprocessing/popen_fork.py

@@ -25,7 +25,7 @@ class Popen(object):
         if self.returncode is None:
             try:
                 pid, sts = os.waitpid(self.pid, flag)
-            except OSError as e:
+            except OSError:
                 # Child process not yet created. See #1731717
                 # e.errno == errno.ECHILD == 10
                 return None

Lib/poplib.py

@@ -385,7 +385,7 @@ class POP3:
             for capline in rawcaps:
                 capnm, capargs = _parsecap(capline)
                 caps[capnm] = capargs
-        except error_proto as _err:
+        except error_proto:
             raise error_proto('-ERR CAPA not supported by server')
         return caps
 

Lib/test/pythoninfo.py

@@ -754,7 +754,7 @@ def collect_info(info):
     ):
         try:
             collect_func(info_add)
-        except Exception as exc:
+        except Exception:
             error = True
             print("ERROR: %s() failed" % (collect_func.__name__),
                   file=sys.stderr)

Lib/test/test_cgitb.py

@@ -31,7 +31,7 @@ class TestCgitb(unittest.TestCase):
     def test_text(self):
         try:
             raise ValueError("Hello World")
-        except ValueError as err:
+        except ValueError:
             text = cgitb.text(sys.exc_info())
             self.assertIn("ValueError", text)
             self.assertIn("Hello World", text)

Lib/test/test_class.py

@@ -529,7 +529,7 @@ class ClassTests(unittest.TestCase):
             # In debug mode, printed XXX undetected error and
             #  raises AttributeError
             I()
-        except AttributeError as x:
+        except AttributeError:
             pass
         else:
             self.fail("attribute error for I.__init__ got masked")

Lib/test/test_codecs.py

@@ -11,7 +11,7 @@ from test import support
 
 try:
     import _testcapi
-except ImportError as exc:
+except ImportError:
     _testcapi = None
 
 try:

Lib/test/test_decimal.py

@@ -5600,13 +5600,13 @@ class SignatureTest(unittest.TestCase):
                     args, kwds = mkargs(C, c_sig)
                     try:
                         getattr(c_type(9), attr)(*args, **kwds)
-                    except Exception as err:
+                    except Exception:
                         raise TestFailed("invalid signature for %s: %s %s" % (c_func, args, kwds))
 
                     args, kwds = mkargs(P, p_sig)
                     try:
                         getattr(p_type(9), attr)(*args, **kwds)
-                    except Exception as err:
+                    except Exception:
                         raise TestFailed("invalid signature for %s: %s %s" % (p_func, args, kwds))
 
         doit('Decimal')

Lib/test/test_ftplib.py

@@ -346,7 +346,7 @@ if ssl is not None:
                 if err.args[0] in (ssl.SSL_ERROR_WANT_READ,
                                    ssl.SSL_ERROR_WANT_WRITE):
                     return
-            except OSError as err:
+            except OSError:
                 # Any "socket error" corresponds to a SSL_ERROR_SYSCALL return
                 # from OpenSSL's SSL_shutdown(), corresponding to a
                 # closed socket condition. See also:

Lib/test/test_sys_settrace.py

@@ -161,8 +161,8 @@ def raises():
 def test_raise():
     try:
         raises()
-    except Exception as exc:
-        x = 1
+    except Exception:
+        pass
 
 test_raise.events = [(0, 'call'),
                      (1, 'line'),
@@ -191,7 +191,7 @@ def _settrace_and_raise(tracefunc):
 def settrace_and_raise(tracefunc):
     try:
         _settrace_and_raise(tracefunc)
-    except RuntimeError as exc:
+    except RuntimeError:
         pass
 
 settrace_and_raise.events = [(2, 'exception'),

Lib/test/test_time.py

@@ -825,7 +825,7 @@ class CPyTimeTestCase:
                     try:
                         result = pytime_converter(value, time_rnd)
                         expected = expected_func(value)
-                    except Exception as exc:
+                    except Exception:
                         self.fail("Error on timestamp conversion: %s" % debug_info)
                     self.assertEqual(result,
                                      expected,

Lib/test/test_traceback.py

@@ -313,7 +313,7 @@ class TracebackFormatTests(unittest.TestCase):
         with captured_output("stderr") as stderr_f:
             try:
                 f()
-            except RecursionError as exc:
+            except RecursionError:
                 render_exc()
             else:
                 self.fail("no recursion occurred")
@@ -360,7 +360,7 @@ class TracebackFormatTests(unittest.TestCase):
         with captured_output("stderr") as stderr_g:
             try:
                 g()
-            except ValueError as exc:
+            except ValueError:
                 render_exc()
             else:
                 self.fail("no value error was raised")
@@ -396,7 +396,7 @@ class TracebackFormatTests(unittest.TestCase):
         with captured_output("stderr") as stderr_h:
             try:
                 h()
-            except ValueError as exc:
+            except ValueError:
                 render_exc()
             else:
                 self.fail("no value error was raised")
@@ -424,7 +424,7 @@ class TracebackFormatTests(unittest.TestCase):
         with captured_output("stderr") as stderr_g:
             try:
                 g(traceback._RECURSIVE_CUTOFF)
-            except ValueError as exc:
+            except ValueError:
                 render_exc()
             else:
                 self.fail("no error raised")
@@ -452,7 +452,7 @@ class TracebackFormatTests(unittest.TestCase):
         with captured_output("stderr") as stderr_g:
             try:
                 g(traceback._RECURSIVE_CUTOFF + 1)
-            except ValueError as exc:
+            except ValueError:
                 render_exc()
             else:
                 self.fail("no error raised")

Lib/test/test_urllib2net.py

@@ -199,7 +199,7 @@ class OtherNetworkTests(unittest.TestCase):
             try:
                 with urllib.request.urlopen(URL) as res:
                     pass
-            except ValueError as e:
+            except ValueError:
                 self.fail("urlopen failed for site not sending \
                            Connection:close")
             else:

Lib/test/test_uuid.py

@@ -471,7 +471,7 @@ class BaseTestUUID:
         # the value from too_large_getter above.
         try:
             self.uuid.uuid1(node=node)
-        except ValueError as e:
+        except ValueError:
             self.fail('uuid1 was given an invalid node ID')
 
     def test_uuid1(self):

Lib/unittest/case.py

@@ -712,7 +712,7 @@ class TestCase(object):
             function, args, kwargs = cls._class_cleanups.pop()
             try:
                 function(*args, **kwargs)
-            except Exception as exc:
+            except Exception:
                 cls.tearDown_exceptions.append(sys.exc_info())
 
     def __call__(self, *args, **kwds):

Lib/urllib/request.py

@@ -1778,7 +1778,7 @@ class URLopener:
                 hdrs = fp.info()
                 fp.close()
                 return url2pathname(_splithost(url1)[1]), hdrs
-            except OSError as msg:
+            except OSError:
                 pass
         fp = self.open(url, data)
         try:

Lib/xml/sax/__init__.py

@@ -78,7 +78,7 @@ def make_parser(parser_list=()):
     for parser_name in list(parser_list) + default_parser_list:
         try:
             return _create_parser(parser_name)
-        except ImportError as e:
+        except ImportError:
             import sys
             if parser_name in sys.modules:
                 # The parser module was found, but importing it