Given:

class BadRepr:
    def __repr__(self):
        raise Exception('repr_exc')


obj = BadRepr()

__import__('pdb').set_trace()

(Pdb) p obj
(Pdb) pp obj
(Pdb)

Possible patch - clumsy due to self._getval both printing any error already, and raising the exception:

diff --git i/Lib/pdb.py w/Lib/pdb.py
index f5d33c27fc..59a419d961 100755
--- i/Lib/pdb.py
+++ w/Lib/pdb.py
@@ -1177,18 +1177,28 @@ def do_p(self, arg):
         Print the value of the expression.
         """
         try:
-            self.message(repr(self._getval(arg)))
+            val = self._getval(arg)
         except:
-            pass
+            return
+        try:
+            self.message(repr(val))
+        except:
+            exc_info = sys.exc_info()[:2]
+            self.error(traceback.format_exception_only(*exc_info)[-1].strip())

     def do_pp(self, arg):
         """pp expression
         Pretty-print the value of the expression.
         """
         try:
-            self.message(pprint.pformat(self._getval(arg)))
+            val = self._getval(arg)
         except:
-            pass
+            return
+        try:
+            self.message(pprint.pformat(val))
+        except:
+            exc_info = sys.exc_info()[:2]
+            self.error(traceback.format_exception_only(*exc_info)[-1].strip())

     complete_print = _complete_expression
     complete_p = _complete_expression

Hi Daniel, this is indeed unexpected, I don't see how to have a better patch since the fact that _getval() raise an exception is used in do_source() and do_whatis().

Could you convert your patch as a PR and add a test?

Thanks for the feedback.

What do you think of refactoring the common block (also used in other places) into a method?

+ except:
+ exc_info = sys.exc_info()[:2]
+ self.error(traceback.format_exception_only(*exc_info)[-1].strip())

This could/should be done separately probably then, just want your opinion on it. This would also allow to customize/override it in a single place then (e.g. with pdbpp I am displaying tracebacks for errors, which is done via error() currently then).

This part of the code is already used in three places and your patch would add two occurrences of of it, I think it would be great to put the part that print the exception in a private method, to avoid duplicating it all over the place.

Doing this seems small enough to me that I think it could be done in the same PR to avoid the overhead of having two separates PRs.

New changeset 6544b25 by Daniel Hahler in branch 'main':
bpo-37022: Fix bug where pdb's do_p/do_pp commands swallow exceptions from repr (GH-18180)
6544b25

New changeset e3bc32f by Miss Islington (bot) in branch '3.10':
bpo-37022: Fix bug where pdb's do_p/do_pp commands swallow exceptions from repr (GH-18180) (GH-26650)
e3bc32f

New changeset 175ebc6 by Miss Islington (bot) in branch '3.9':
bpo-37022: Fix bug where pdb's do_p/do_pp commands swallow exceptions from repr (GH-18180) (GH-26651)
175ebc6