On 7/9/19, Steve Barnes <gadgetst...@live.co.uk> wrote:
>
> Currently the py[w] command will launch the latest python by default however
> I feel that this discourages the testing of pre-releases & release
> candidates as once they are installed they will become the default. What I
> would like is for the default to be the highest version number of a full
> release but the user to be able to specify a specific version even if it is
> a pre-release.
With the existing launcher, if we install a pre-release candidate, we
can set the PY_PYTHON environment variable to make the launcher
default to a preferred stable release.
To modify the launcher to detect a "final" build, we can check the
file version from the PE image's FIXEDFILEINFO [1]. It consists of
four 16-bit values: PY_MAJOR_VERSION, PY_MINOR_VERSION, FIELD3,
PYTHON_API_VERSION. What we want is FIELD3, which is the upper WORD in
the least significant DWORD (i.e. dwFileVersionLS >> 16). FIELD3 is
computed as
micro * 1000 + levelnum * 10 + serial
where levelnum is
alpha: 10
beta: 11
candidate: 12
final: 15
and serial is 0-9. The executable is a "final" release if FIELD3
modulo 1000 is at least 150. Here's a quick ctypes example with Python
3.7.3:
version = ctypes.WinDLL('version', use_last_error=True)
szBlock = version.GetFileVersionInfoSizeW(sys.executable, None)
block = (ctypes.c_char * szBlock)()
version.GetFileVersionInfoW(sys.executable, 0, szBlock, block)
pinfo = ctypes.POINTER(ctypes.c_ulong)()
szInfo = ctypes.c_ulong()
version.VerQueryValueW(block, '\\', ctypes.byref(pinfo),
ctypes.byref(szInfo))
>>> (pinfo[3] >> 16) % 1000
150
>>> sys.version_info
sys.version_info(major=3, minor=7, micro=3, releaselevel='final', serial=0)
[1]:
https://docs.microsoft.com/en-us/windows/win32/api/verrsrc/ns-verrsrc-tagvs_fixedfileinfo
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