Print from background thread has broken line endings #129385
Description
Bug report
Bug description:
I noticed that in python 3.13 (in linux), messages that were previously logged nicely to the console are now behaving as if the lines end like a windows line feed character without carriage return -- the cursor moves down a row, but not back to the beginning of the line. The example I chose below looks tame, but it makes most real logging output very difficult to read.
This only seems to happen for lines printed from background threads:
import threading, time
def msg():
print('this is line 1')
print('this is line 2')
time.sleep(0.1) # first few lines work as expected, but after a brief time, the problem begins
print('this is line 3')
print('this is line 4')
thread = threading.Thread(target=msg)
thread.start()Running this code in python 3.13.1, interactive mode looks like:
$ python -i print_test.py
this is line 1
this is line 2
>>> this is line 3
this is line 4
>>>
Non-interactive looks fine:
$ python print_test.py
this is line 1
this is line 2
this is line 3
this is line 4
And interactive in 3.12.8 looks fine:
$ python -i print_test.py
this is line 1
this is line 2
>>> this is line 3
this is line 4
CPython versions tested on:
3.13
Operating systems tested on:
Linux