gh-138641: prevent accessing non-existing curframe in pdb commands

Lib/pdb.py

@@ -925,6 +925,9 @@ def _read_code(self, line):
         return code, buffer, is_await_code
 
     def default(self, line):
+        if not self.curframe:
+            self.error("No current frame.")
+            return
         if line[:1] == '!': line = line[1:].strip()
         locals = self.curframe.f_locals
         globals = self.curframe.f_globals
@@ -1181,6 +1184,7 @@ def complete_multiline_names(self, text, line, begidx, endidx):
         return self.completedefault(text, line, begidx, endidx)
 
     def completedefault(self, text, line, begidx, endidx):
+        assert self.curframe is not None
         if text.startswith("$"):
             # Complete convenience variables
             conv_vars = self.curframe.f_globals.get('__pdb_convenience_variables', {})
@@ -1408,6 +1412,9 @@ def do_break(self, arg, temporary=False):
     # To be overridden in derived debuggers
     def defaultFile(self):
         """Produce a reasonable default."""
+        if self.curframe is None:
+            self.error("No current frame.")
+            return None
         filename = self.curframe.f_code.co_filename
         if filename == '<string>' and self.mainpyfile:
             filename = self.mainpyfile
@@ -1946,6 +1953,9 @@ def do_debug(self, arg):
         if not arg:
             self._print_invalid_arg(arg)
             return
+        if not self.curframe:
+            self.error('No current frame.')
+            return
         self.stop_trace()
         globals = self.curframe.f_globals
         locals = self.curframe.f_locals
@@ -2108,6 +2118,9 @@ def do_list(self, arg):
         exception was originally raised or propagated is indicated by
         ">>", if it differs from the current line.
         """
+        if not self.curframe:
+            self.error('No current frame.')
+            return
         self.lastcmd = 'list'
         last = None
         if arg and arg != '.':
@@ -2153,6 +2166,9 @@ def do_longlist(self, arg):
         if arg:
             self._print_invalid_arg(arg)
             return
+        if not self.curframe:
+            self.error('No current frame.')
+            return
         filename = self.curframe.f_code.co_filename
         breaklist = self.get_file_breaks(filename)
         try:

Misc/NEWS.d/next/Library/2025-09-08-17-50-33.gh-issue-138641.nBPvKe.rst

@@ -0,0 +1 @@
+Fix: breakpoint() in pdb can cause crash.