input() not including built-in newline if string > 236 characters

[vv0bbLeS]

Bug report

Bug description:

When using input() in the REPL, the behavior is not as expected if the string is > 236 characters (in fact, the input text disappears entirely).

#=====
# string = 236 characters

s = """wow this is a really long sentence, like really who types a sentence this long, but i guess if you have something to say that's important and it takes a long time to say, you can write a long sentence for it, especially if shorter works"""

input(s)  # expected behavior - this shows the text to the user during input

#=====
# string > 236 characters

s = """wow this is a really long sentence, like really who types a sentence this long, but i guess if you have something to say that's important and it takes a long time to say, you can write a long sentence for it, especially if shorter works and you need more text"""

input(s)  # unexpected behavior - this does not show the text to the user during input

#=====
# string > 236 characters, with manual newline added

s = """wow this is a really long sentence, like really who types a sentence this long, but i guess if you have something to say that's important and it takes a long time to say, you can write a long sentence for it, especially if shorter works and you need more text\n"""

input(s)  # unexpected behavior - this shows the text to the user, but the prompt is not at the end of the string

CPython versions tested on:

3.13

Operating systems tested on:

Windows

[StanFromIreland]

This is only in the repl from what I can tell, it does not occur when running a script.

I guess it may also have something to do with the core implementation so probably interpreter-core and topic-repl would be best here.

[picnixz]

Does it happen with the old REPL as well? Namely what happens when using PYTHON_BASIC_REPL=1 python?

[picnixz]

What happens with short inputs ending with a new line? does it also behave weirdly? also is 236 characters the width of your terminal?

[StanFromIreland]

Works fine with old repl.

I am not sure what the user means by the newline however. Short strings work fine.

[picnixz]

I am not sure what the user means by the newline however

There is a \n in the last prompt input.

[StanFromIreland]

This is the old repl:

>>> s = """wow this is a really long sentence, like really who types a sentence this long, but i guess if you have something to say that's important and it takes a long time to say, you can write a long sentence for it, especially if shorter works and you need more text"""
>>> input(s)
wow this is a really long sentence, like really who types a sentence this long, but i guess if you have something to say that's important and it takes a long time to say, you can write a long sentence for it, especially if shorter works and you need more textd
'd'

[picnixz]

The old REPL seems to work 🤔 @encukou did you remove the labels because you think it's an issue with input()?

[tomasr8]

The problem seems to be somewhere in this method:

cpython/Lib/_pyrepl/reader.py

Line 323 in e82c2ca

def calc_screen(self) -> list[str]:

When the prompt is narrower than the terminal width it's printed inside this if:

cpython/Lib/_pyrepl/reader.py

Lines 381 to 385 in e82c2ca

	if wrapcount == 0:
	offset += ll + 1 # Takes all of the line plus the newline
	last_refresh_line_end_offsets.append(offset)
	screen.append(prompt + l)
	screeninfo.append((lp, l2))

Otherwise the else branch is taken but in this case l=='' so the while loop is never entered:

cpython/Lib/_pyrepl/reader.py

Lines 386 to 391 in e82c2ca

	else:
	i = 0
	while l:
	prelen = lp if i == 0 else 0
	index_to_wrap_before = 0
	column = 0

I could get it to print the prompt, but then the cursor position was wrong for some reason..