gh-130698: Add safe methods to get prompts for new REPL

Lib/_pyrepl/main.py

@@ -47,10 +47,11 @@ def interactive_console(mainmodule=None, quiet=False, pythonstartup=False):
 
     # set sys.{ps1,ps2} just before invoking the interactive interpreter. This
     # mimics what CPython does in pythonrun.c
+    from .utils import DEFAULT_PS1, DEFAULT_PS2
     if not hasattr(sys, "ps1"):
-        sys.ps1 = ">>> "
+        sys.ps1 = DEFAULT_PS1
     if not hasattr(sys, "ps2"):
-        sys.ps2 = "... "
+        sys.ps2 = DEFAULT_PS2
 
     from .console import InteractiveColoredConsole
     from .simple_interact import run_multiline_interactive_console

Lib/_pyrepl/reader.py

@@ -28,6 +28,8 @@
 from dataclasses import dataclass, field, fields
 
 from . import commands, console, input
+from .utils import DEFAULT_PS1
+from .utils import MULTILINE_PS2, MULTILINE_PS3, MULTILINE_PS4
 from .utils import wlen, unbracket, disp_str, gen_colors, THEME
 from .trace import trace
 
@@ -473,22 +475,40 @@ def get_arg(self, default: int = 1) -> int:
             return default
         return self.arg
 
+    @staticmethod
+    def __get_prompt_str(prompt: object, default_prompt: str) -> str:
+        """
+        Convert prompt object to string.
+
+        If str(prompt) raises BaseException, MemoryError or SystemError then stop
+        the REPL. For other exceptions return default_prompt.
+        """
+        try:
+            return str(prompt)
+        except (MemoryError, SystemError):
+            raise
+        except Exception:
+            return default_prompt
+
     def get_prompt(self, lineno: int, cursor_on_line: bool) -> str:
         """Return what should be in the left-hand margin for line
         'lineno'."""
         if self.arg is not None and cursor_on_line:
-            prompt = f"(arg: {self.arg}) "
+            prompt = DEFAULT_PS1
+            arg = self.__get_prompt_str(self.arg, "")
+            if arg:
+                prompt = f"(arg: {self.arg}) "
         elif self.paste_mode:
             prompt = "(paste) "
         elif "\n" in self.buffer:
             if lineno == 0:
-                prompt = self.ps2
+                prompt = self.__get_prompt_str(self.ps2, MULTILINE_PS2)
             elif self.ps4 and lineno == self.buffer.count("\n"):
-                prompt = self.ps4
+                prompt = self.__get_prompt_str(self.ps4, MULTILINE_PS4)
             else:
-                prompt = self.ps3
+                prompt = self.__get_prompt_str(self.ps3, MULTILINE_PS3)
         else:
-            prompt = self.ps1
+            prompt = self.__get_prompt_str(self.ps1, DEFAULT_PS1)
 
         if self.can_colorize:
             t = THEME()

Lib/_pyrepl/readline.py

@@ -40,6 +40,7 @@
 from .completing_reader import CompletingReader
 from .console import Console as ConsoleType
 from ._module_completer import ModuleCompleter, make_default_module_completer
+from .utils import MULTILINE_PS4
 
 Console: type[ConsoleType]
 _error: tuple[type[Exception], ...] | type[Exception]
@@ -390,7 +391,7 @@ def multiline_input(self, more_lines: MoreLinesCallable, ps1: str, ps2: str) ->
             reader.ps1 = ps1
             reader.ps2 = ps1
             reader.ps3 = ps2
-            reader.ps4 = ""
+            reader.ps4 = MULTILINE_PS4
             with warnings.catch_warnings(action="ignore"):
                 return reader.readline()
         finally:

Lib/_pyrepl/simple_interact.py

@@ -34,6 +34,7 @@
 import errno
 
 from .readline import _get_reader, multiline_input, append_history_file
+from .utils import DEFAULT_PS1, DEFAULT_PS2
 
 
 _error: tuple[type[Exception], ...] | type[Exception]
@@ -137,8 +138,8 @@ def maybe_run_command(statement: str) -> bool:
             except Exception:
                 pass
 
-            ps1 = getattr(sys, "ps1", ">>> ")
-            ps2 = getattr(sys, "ps2", "... ")
+            ps1 = getattr(sys, "ps1", DEFAULT_PS1)
+            ps2 = getattr(sys, "ps2", DEFAULT_PS2)
             try:
                 statement = multiline_input(more_lines, ps1, ps2)
             except EOFError:

Lib/_pyrepl/utils.py

@@ -59,6 +59,16 @@ class ColorSpan(NamedTuple):
     tag: str
 
 
+DEFAULT_PS1 = ">>> "
+DEFAULT_PS2 = "... "
+
+# mimics behavior of _ReadlineWrapper.multiline
+MULTILINE_PS1 = DEFAULT_PS1
+MULTILINE_PS2 = DEFAULT_PS1
+MULTILINE_PS3 = DEFAULT_PS2
+MULTILINE_PS4 = ""
+
+
 @functools.cache
 def str_width(c: str) -> int:
     if ord(c) < 128:

Lib/asyncio/__main__.py

@@ -14,6 +14,7 @@
 
 from _colorize import get_theme
 from _pyrepl.console import InteractiveColoredConsole
+from _pyrepl.utils import DEFAULT_PS1
 
 from . import futures
 
@@ -103,7 +104,7 @@ def run(self):
                     startup_code = compile(f.read(), startup_path, "exec")
                     exec(startup_code, console.locals)
 
-            ps1 = getattr(sys, "ps1", ">>> ")
+            ps1 = getattr(sys, "ps1", DEFAULT_PS1)
             if CAN_USE_PYREPL:
                 theme = get_theme().syntax
                 ps1 = f"{theme.prompt}{ps1}{theme.reset}"

Lib/code.py

@@ -217,17 +217,18 @@ def interact(self, banner=None, exitmsg=None):
         a default message is printed.
 
         """
+        from _pyrepl.utils import DEFAULT_PS1, DEFAULT_PS2
         try:
             sys.ps1
             delete_ps1_after = False
         except AttributeError:
-            sys.ps1 = ">>> "
+            sys.ps1 = DEFAULT_PS1
             delete_ps1_after = True
         try:
             sys.ps2
             delete_ps2_after = False
         except AttributeError:
-            sys.ps2 = "... "
+            sys.ps2 = DEFAULT_PS2
             delete_ps2_after = True
 
         cprt = 'Type "help", "copyright", "credits" or "license" for more information.'

Lib/test/test_pyrepl/support.py

@@ -6,7 +6,7 @@
 from _pyrepl.console import Console, Event
 from _pyrepl.readline import ReadlineAlikeReader, ReadlineConfig
 from _pyrepl.simple_interact import _strip_final_indent
-from _pyrepl.utils import unbracket, ANSI_ESCAPE_SEQUENCE
+from _pyrepl.utils import unbracket, ANSI_ESCAPE_SEQUENCE, DEFAULT_PS1, DEFAULT_PS2
 
 
 class ScreenEqualMixin:
@@ -22,8 +22,8 @@ def multiline_input(reader: ReadlineAlikeReader, namespace: dict | None = None):
     saved = reader.more_lines
     try:
         reader.more_lines = partial(more_lines, namespace=namespace)
-        reader.ps1 = reader.ps2 = ">>> "
-        reader.ps3 = reader.ps4 = "... "
+        reader.ps1 = reader.ps2 = DEFAULT_PS1
+        reader.ps3 = reader.ps4 = DEFAULT_PS2
         return reader.readline()
     finally:
         reader.more_lines = saved

Lib/test/test_pyrepl/test_reader.py

@@ -11,9 +11,28 @@
 from .support import prepare_reader, prepare_console
 from _pyrepl.console import Event
 from _pyrepl.reader import Reader
+from _pyrepl.utils import DEFAULT_PS1
+from _pyrepl.utils import MULTILINE_PS1, MULTILINE_PS2, MULTILINE_PS3, MULTILINE_PS4
 from _colorize import default_theme
 
 
+def prepare_reader_with_prompt(
+    console, ps1=MULTILINE_PS1, ps2=MULTILINE_PS2, ps3=MULTILINE_PS3, ps4=MULTILINE_PS4):
+    reader = prepare_reader(
+        console,
+        can_colorize=False,
+        paste_mode=False,
+        ps1=ps1,
+        ps2=ps2,
+        ps3=ps3,
+        ps4=ps4
+    )
+
+    # we should use original get_prompt from reader to get exceptions
+    del reader.get_prompt
+    return reader
+
+
 overrides = {"reset": "z", "soft_keyword": "K"}
 colors = {overrides.get(k, k[0].lower()): v for k, v in default_theme.syntax.items()}
 
@@ -39,10 +58,10 @@ def test_calc_screen_prompt_handling(self):
         def prepare_reader_keep_prompts(*args, **kwargs):
             reader = prepare_reader(*args, **kwargs)
             del reader.get_prompt
-            reader.ps1 = ">>> "
-            reader.ps2 = ">>> "
-            reader.ps3 = "... "
-            reader.ps4 = ""
+            reader.ps1 = MULTILINE_PS1
+            reader.ps2 = MULTILINE_PS2
+            reader.ps3 = MULTILINE_PS3
+            reader.ps4 = MULTILINE_PS4
             reader.can_colorize = False
             reader.paste_mode = False
             return reader
@@ -300,6 +319,89 @@ def test_prompt_length(self):
         self.assertEqual(prompt, "\033[0;32m樂>\033[0m> ")
         self.assertEqual(l, 5)
 
+    def test_prompt_ps1_raise_exception(self):
+        # Handles exceptions from ps1 prompt
+        class Prompt:
+            def __str__(self): 1/0
+
+        _prepare_reader = functools.partial(
+            prepare_reader_with_prompt,
+            ps1=Prompt(),
+        )
+
+        reader, _ = handle_all_events(
+            events=code_to_events("a=1"),
+            prepare_reader=_prepare_reader
+        )
+
+        prompt = reader.get_prompt(0, False)
+        self.assertEqual(prompt, DEFAULT_PS1)
+
+    def test_prompt_ps2_ps3_ps4_raise_exception(self):
+        # Handles exceptions from ps2, ps3 and ps4 prompts
+        class Prompt:
+            def __str__(self): 1/0
+
+        _prepare_reader = functools.partial(
+            prepare_reader_with_prompt,
+            ps1=Prompt(),
+            ps2=Prompt(),
+            ps3=Prompt(),
+            ps4=Prompt(),
+        )
+
+        reader, _ = handle_all_events(
+            events=code_to_events("if cond:\nfunc()\nfunc()"),
+            prepare_reader=_prepare_reader
+        )
+
+        prompt = reader.get_prompt(0, False)
+        self.assertEqual(prompt, MULTILINE_PS2)
+
+        prompt = reader.get_prompt(1, False)
+        self.assertEqual(prompt, MULTILINE_PS3)
+
+        prompt = reader.get_prompt(2, False)
+        self.assertEqual(prompt, MULTILINE_PS4)
+
+    def test_prompt_arg_raise_exception(self):
+        # Handles exceptions from arg prompt
+        class Prompt:
+            def __str__(self): 1/0
+            def __rmul__(self, b): return b
+
+        reader, _ = handle_all_events(
+            events=code_to_events("if some_condition:\nsome_function()"),
+            prepare_reader=prepare_reader_with_prompt,
+        )
+
+        reader.arg = Prompt()
+        prompt = reader.get_prompt(0, True)
+        self.assertEqual(prompt, DEFAULT_PS1)
+
+    def test_prompt_raise_exception(self):
+        # Tests unrecoverable exceptions from prompts
+        cases = [
+            (MemoryError, "No memory for prompt"),
+            (SystemError, "System error for prompt"),
+        ]
+        for cls, msg in cases:
+            with self.subTest(msg):
+
+                class Prompt:
+                    def __str__(self): raise cls(msg)
+
+                _prepare_reader = functools.partial(
+                    prepare_reader_with_prompt,
+                    ps1=Prompt(),
+                )
+
+                with self.assertRaisesRegex(cls, msg):
+                    handle_events_narrow_console(
+                        events=code_to_events("a=1"),
+                        prepare_reader=_prepare_reader,
+                    )
+
     def test_completions_updated_on_key_press(self):
         namespace = {"itertools": itertools}
         code = "itertools."

Misc/NEWS.d/next/Library/2025-03-13-00-39-54.gh-issue-130698.o2aU3e.rst

@@ -0,0 +1 @@
+Avoid exiting the new REPL when prompt object raises an exception.