[print()] did not print all the the numbers expected

[2930627136]

Bug report

Bug description:

the output is wrong:

should be 1,2,3,4,5,6,7,8,9,

CPython versions tested on:

3.13

Operating systems tested on:

Windows

[skirpichev]

I can't reproduce this on Linux, that's what I see:

>>> a=1
>>> a
1
>>> while a<10:
...     print(a, end=',')
...     a+=1
...     
1,2,3,4,5,6,7,8,9,>>> 

Are you using new REPL? Could you please try to reproduce with PYTHON_BASIC_REPL environment variable set? (I.e. with old repl.)

[JanEricNitschke]

I can reproduce it on windows:

C:\Windows\system32>uv run --python 3.13 python
Python 3.13.1 (main, Jan 14 2025, 22:47:35) [MSC v.1942 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a=1
>>> a
1
>>> while a<10:
...     print(a,end=',')
...     a+=1
...
>>> 3,4,5,6,7,8,9,

Old repl works:

C:\Windows\system32>set PYTHON_BASIC_REPL=1

C:\Windows\system32>uv run --python 3.13 python
Python 3.13.1 (main, Jan 14 2025, 22:47:35) [MSC v.1942 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a=1
>>> a
1
>>> while a<10:
...     print(a, end=',')
...     a+=1
...
1,2,3,4,5,6,7,8,9,>>>

[JanEricNitschke]

Also still there in 3.14:

C:\Windows\system32>uv run --python 3.14.0a4 python
Python 3.14.0a4 (main, Jan 14 2025, 22:47:21) [MSC v.1942 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a=1
>>> a
1
>>> while a<10:
...     print(a, end=',')
...     a+=1
...
>>> 3,4,5,6,7,8,9,

and current main:

PS D:\Programming\Projects\cpython> .\PCbuild\amd64\python_d.exe
Python 3.15.0a0 (heads/main-dirty:5edfe55acf, Sep  9 2025, 07:47:38) [MSC v.1944 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a=1
>>> a
1
>>> while a<10:
...     print(a, end=',')
...     a+=1
...
>>> 3,4,5,6,7,8,9,

[sergey-miryanov]

I believe it is known issue - #128067