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