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

[sergey-miryanov]

It fixes cases when ps1, ps2, ps3, ps4 raise exception from __str__.

This PR still misses tests for Reader.arg, but maybe you can review the whole solution - do I drive in the right direction?
Fixed for Reader.arg.

• Issue: REPL exits with traceback when str(sys.ps1) raises #130698

[tomasr8]

Should these match?

cpython/Lib/_pyrepl/reader.py

Lines 196 to 199 in 95800fe

	ps1: str = "->> "
	ps2: str = "/>> "
	ps3: str = "|.. "
	ps4: str = R"\__ "

[sergey-miryanov]

No, I believe this is should be like:

DEFAULT_PS1 = ">>> "
DEFAULT_PS2 = ">>> "
DEFAULT_PS3 = "... "
DEFAULT_PS4 = "... "

I had misread this

cpython/Lib/_pyrepl/reader.py

Lines 171 to 179 in 71da68d

	* ps1, ps2, ps3, ps4:
	prompts. ps1 is the prompt for a one-line input; for a
	multiline input it looks like:
	ps2> first line of input goes here
	ps3> second and further
	ps3> lines get ps3
	...
	ps4> and the last one gets ps4
	As with the usual top-level, you can set these to instances if

[tomasr8]

We could use a slightly simpler setup code:

Suggested change

	def prepare_reader_keep_prompts(*args, **kwargs):
	reader = prepare_reader(*args, **kwargs)
	del reader.get_prompt
	reader.ps1 = Prompt()
	reader.ps2 = "... "
	reader.ps3 = "... "
	reader.ps4 = ""
	reader.can_colorize = False
	reader.paste_mode = False
	return reader
	events = code_to_events("a=1")
	reader, _ = handle_events_narrow_console(
	events,
	prepare_reader=prepare_reader_keep_prompts,
	)
	def prepare_reader(events):
	console = FakeConsole(events)
	config = ReadlineConfig(readline_completer=None)
	reader = ReadlineAlikeReader(console=console, config=config)
	reader.can_colorize = False
	return reader
	events = code_to_events("if some_condition:\nsome_function()")
	reader = prepare_reader(events)

[sergey-miryanov]

Unfortunately this doesn't simplify code. I have added more simpler one on my sight. Note, we should use handle_all_events (or handle_events_narrow_console) to process whole input string and get it in the reader.buffer to check if '\n' contains or not in buffer.