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blueyed wants to merge 3 commits into from
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bpo-36550: pdb/cmd: avoid creating exceptions #4666

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pdb/cmd: avoid creating exceptions
blueyed Dec 1, 2017
d2470f5
Merge branch 'main' into pdb-avoid-exc
hauntsaninja Feb 26, 2023
e843f35
Merge branch 'main' into pdb-avoid-exc
arhadthedev Apr 30, 2023
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9 changes: 4 additions & 5 deletions Lib/cmd.py
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Original file line number Diff line number Diff line change
Expand Up @@ -210,11 +210,10 @@ def onecmd(self, line):
if cmd == '':
return self.default(line)
else:
try:
func = getattr(self, 'do_' + cmd)
except AttributeError:
return self.default(line)
return func(arg)
func = getattr(self, 'do_' + cmd, None)
if func is not None:
return func(arg)
return self.default(line)
Comment on lines +213 to +216

@serhiy-storchaka serhiy-storchaka Aug 25, 2021

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Would this work too?

            try:
                func = getattr(self, 'do_' + cmd)
            except AttributeError:
                pass  # restore the original sys.exc_info()
            else:
                return func(arg)
            return self.default(line)

I do not suggest this code, just ask.

@iritkatriel iritkatriel Aug 25, 2021

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I think it works if you add a naked raise at the end of the except block. Try this:

try:
   raise ValueError(1)
except:
   try:
      raise AttributeError(2)
   except AttributeError:
      pass
   else:
      print(42)
   raise
else:
  print(53)

@iritkatriel iritkatriel Aug 25, 2021

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In something like pdb you would need to check if there is an active exception. Something like this:

import sys

def maybe_reraise():
   if sys.exc_info() != (None, None, None):
       raise

try:
   raise ValueError(1)
except:
   try:
      raise AttributeError(2)
   except AttributeError:
      pass
   else:
      print(42)
   maybe_reraise()
else:
  print(53)

@iritkatriel iritkatriel Aug 25, 2021

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Sorry, I missed the point - we don't want to raise the exception, just to restore it. In that case doesn't my example show that there is no issue?

I'm not sure this PR is needed after all. If we had a test we would know, but since @blueyed is no longer responding we may need to just close it until an actual bug is reported.


def emptyline(self):
"""Called when an empty line is entered in response to the prompt.
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5 changes: 1 addition & 4 deletions Lib/pdb.py
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Original file line number Diff line number Diff line change
Expand Up @@ -508,10 +508,7 @@ def handle_command_def(self, line):
else:
cmdlist.append(cmd)
# Determine if we must stop
try:
func = getattr(self, 'do_' + cmd)
except AttributeError:
func = self.default
func = getattr(self, 'do_' + cmd, self.default)
# one of the resuming commands
if func.__name__ in self.commands_resuming:
self.commands_doprompt[self.commands_bnum] = False
Expand Down