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

Author: pablogsal

Lib/asynchat.py

@@ -117,7 +117,7 @@ def handle_read(self):
             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 @@ async def _sock_sendfile_native(self, sock, file, offset, count):
             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 @@ async def create_unix_server(
     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 @@ async def _sock_sendfile_native(self, sock, file, offset, count):
             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 @@ def _findLib_ld(name):
                 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 @@ def _create_(cls, class_name, names, *, module=None, qualname=None, type=None, s
         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 @@ def phase2(self): # Distinguish files, directories, funnies
             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 @@
     _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 @@ def write_file(self, new_text, filename, old_text, encoding):
             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 @@ def serve_client(self, conn):
                     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 @@ def serve_client(self, conn):
             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 @@ def poll(self, flag=os.WNOHANG):
         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 @@ def _parsecap(line):
             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 @@ def test_html(self):
     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 I:
             # 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 @@
 
 try:
     import _testcapi
-except ImportError as exc:
+except ImportError:
     _testcapi = None
 
 try:

Lib/test/test_decimal.py

@@ -5600,13 +5600,13 @@ def doit(ty):
                     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 @@ def _do_ssl_shutdown(self):
                 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 @@ def convert_values(ns_timestamps):
                     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 @@ def f():
         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 @@ def g(count=10):
         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 @@ def h(count=10):
         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 @@ def h(count=10):
         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 @@ def h(count=10):
         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 @@ def test_sites_no_connection_close(self):
             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 @@ def test_uuid1_eui64(self):
         # 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 @@ def doClassCleanups(cls):
             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 @@ def retrieve(self, url, filename=None, reporthook=None, data=None):
                 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