I close the issue, it has been fixed.


I'm no longer able to reproduce the initial issue:

$ ./configure --with-pydebug --with-valgrind
$ make clean
$ make
$ valgrind --suppressions=Misc/valgrind-python.supp ./python 

==2670== Memcheck, a memory error detector
==2670== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==2670== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==2670== Command: ./python
==2670== 
Python 3.9.0a0 (heads/master:91528f40c3, Oct 23 2019, 01:36:01) 
[GCC 9.2.1 20190827 (Red Hat 9.2.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> exec("")
>>> ^D # CTRL+D
==2670== 
==2670== HEAP SUMMARY:
==2670==     in use at exit: 1,530,371 bytes in 26,288 blocks
==2670==   total heap usage: 49,485 allocs, 23,197 frees, 10,318,174 bytes allocated
==2670== 
==2670== LEAK SUMMARY:
==2670==    definitely lost: 0 bytes in 0 blocks
==2670==    indirectly lost: 0 bytes in 0 blocks
==2670==      possibly lost: 872,665 bytes in 5,936 blocks
==2670==    still reachable: 657,706 bytes in 20,352 blocks
==2670==         suppressed: 0 bytes in 0 blocks
==2670== Rerun with --leak-check=full to see details of leaked memory
==2670== 
==2670== For lists of detected and suppressed errors, rerun with: -s
==2670== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)


Moreover, Python initialization code has been reworked in the PEP 587 implementation to ensure that sys.argv is never empty. If it's called with an empty list, [""] is used instead.