Using double quote around the version argument will cause a failure.

Ex (failure): "py.exe" "-3" "test.py" 
=> run_child: about to run '3" "...\python.exe" "test.py"'
=> ...\python.exe: can't open file '3 test.py': [Errno 22] Invalid argument

Removing the double quote give (success): "py.exe" -3 "test.py" => run_child: about to run '"...\python.exe" "test.py"'

This is mainly problematic when a library or a tool want to be simpler and simply add double quotes around every parameters. This is impossible to do with the python launcher.

The issue seems to come from the PC/launcher.c file. It is the following line in the function process (around line 1622): command += wcslen(p);

This line is suppose to skip the -3 in the command line so that the rest can be given to python as-is. The problem is that while command come from GetCommandLineW and thus contain quote, p come from __wargv and does not contain the double quote. Thus, the 2 characters "- are skipped instead of -3.

I verified this much:
F:\dev\37>py "-3" -m test.test_idle
(null): can't open file '3 -m test.test_idle': [Errno 2] No such file or directory