gh-141295: Persist pdb command history with PyREPL

Doc/library/pdb.rst

@@ -75,6 +75,13 @@ The debugger's prompt is ``(Pdb)``, which is the indicator that you are in debug
    arguments of the ``p`` command.
 
 
+.. versionadded:: 3.16
+   When using PyREPL, debugger commands are saved in ``.python_history.pdb`` in the
+   user's home directory and loaded for subsequent sessions. If
+   :envvar:`PYTHON_HISTORY` is set, its value with ``.pdb`` appended is used
+   instead. Set :envvar:`PYTHON_HISTORY_PDB` to use a different history file.
+
+
 .. _pdb-cli:
 
 Command-line interface

Doc/using/cmdline.rst

@@ -1371,6 +1371,17 @@ conflict.
 
    .. versionadded:: 3.13
 
+.. envvar:: PYTHON_HISTORY_PDB
+
+   Set the location of the command history file used by :mod:`pdb` with
+   PyREPL. By default, it is the value of :envvar:`PYTHON_HISTORY` with ``.pdb``
+   appended, or ``.python_history.pdb`` in the user's home directory if
+   :envvar:`PYTHON_HISTORY` is unset or empty.
+   An empty value also selects the default. This variable is ignored with
+   :option:`-E` or :option:`-I`.
+
+   .. versionadded:: 3.16
+
 .. envvar:: PYTHON_GIL
 
    If this variable is set to ``1``, the global interpreter lock (GIL) will be

Lib/pdb.py

@@ -79,6 +79,7 @@
 import codeop
 import typing
 import inspect
+import warnings
 import builtins
 import itertools
 import linecache
@@ -399,6 +400,22 @@ def __init__(self, pdb_instance, stdin, stdout, prompt):
             )
         )
         self.readline_wrapper.get_reader().gen_colors = self.gen_colors
+        self.history_file = self._get_history_file()
+        self.readline_wrapper.set_history_length(0)
+        try:
+            self.readline_wrapper.read_history_file(self.history_file)
+        except OSError:
+            pass
+
+    @staticmethod
+    def _get_history_file():
+        """Return the pdb history path, defaulting to Python's history plus .pdb."""
+        if not sys.flags.ignore_environment:
+            history = os.environ.get("PYTHON_HISTORY_PDB")
+            if history:
+                return history
+        from site import gethistoryfile
+        return gethistoryfile() + '.pdb'
 
     def readline(self):
 
@@ -425,6 +442,10 @@ def more_lines(text):
                     '... ' + ' ' * (len(self.prompt) - 4)
                 ) + '\n'
             )
+            try:
+                self.readline_wrapper.append_history_file(self.history_file)
+            except (FileNotFoundError, PermissionError, OSError) as e:
+                warnings.warn(f"failed to open the history file for writing: {e}")
             return multiline
         except EOFError:
             return 'EOF'

Lib/test/test_pdb.py

@@ -5393,9 +5393,27 @@ def test_interact_completion(self):
 
 @unittest.skipIf(not pdb._pyrepl_available(), "pyrepl is not available")
 class PdbTestReadlinePyREPL(PdbTestReadline):
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        directory = cls.enterClassContext(os_helper.temp_dir())
+        cls.history_file = os.path.join(directory, 'history')
+
     def _run_pty(self, script, input):
         # Override the env to make sure pyrepl is used in this test class
-        return super()._run_pty(script, input, env={**os.environ})
+        env = os.environ | {'PYTHON_HISTORY_PDB': self.history_file}
+        return super()._run_pty(script, input, env=env)
+
+    def test_history(self):
+        script = "import pdb; pdb.Pdb().set_trace()"
+        os_helper.unlink(self.history_file)
+        self._run_pty(script, b'p 6 * 7\ncontinue\n')
+        with open(self.history_file, encoding='utf-8') as file:
+            self.assertEqual(file.read().splitlines(), ['p 6 * 7', 'continue'])
+
+        # Recall 'continue', then 'p 6 * 7' in a new debugger process.
+        output = self._run_pty(script, b'\x1bOA\x1bOA\ncontinue\n')
+        self.assertIn('42', output)
 
     def test_pyrepl_used(self):
         script = textwrap.dedent("""

Misc/NEWS.d/next/Library/2026-10-20-00-00-00.gh-issue-141295.pdb-history.rst

@@ -0,0 +1,4 @@
+Save and restore :mod:`pdb` command history when using PyREPL. The new
+:envvar:`PYTHON_HISTORY_PDB` environment variable overrides the default
+history path: :envvar:`PYTHON_HISTORY` with ``.pdb`` appended, or
+``.python_history.pdb`` in the user's home directory.

Misc/python.man

@@ -568,6 +568,10 @@ on. Setting it to 0 forces the GIL off. Only available in builds configured
 with \fB\-\-disable\-gil\fP.
 .IP
 This is equivalent to the \fB\-X gil\fR option.
+.IP PYTHON_HISTORY_PDB
+Set the location of the pdb command history file when using PyREPL
+(by default, PYTHON_HISTORY with .pdb appended, or .python_history.pdb in
+the user's home directory).
 .IP PYTHON_HISTORY
 This environment variable can be used to set the location of a history file
 (on Unix, it is \fI~/.python_history\fP by default).

Python/initconfig.c

@@ -525,6 +525,7 @@ static const char usage_envvars[] =
 "                  set to an integer in the range [0,4294967295] to get hash\n"
 "                  values with a predictable seed.\n"
 "#E{PYTHON_HISTORY}  : the location of a .python_history file.\n"
+"#E{PYTHON_HISTORY_PDB}: the location of a .python_history.pdb file used by PyREPL.\n"
 "#E{PYTHONHOME}      : alternate <prefix> directory (or <prefix>#D<exec_prefix>).\n"
 "                  The default module search path uses #H.\n"
 "#E{PYTHONIOENCODING}: encoding[:errors] used for stdin/stdout/stderr\n"