[New-bugs-announce] [issue38506] Launcher for Windows (py.exe) may rank Python 3.xx (in the future) after 3.x

[ynyyn]

New submission from ynyyn <ynyyn at vip.qq.com>:

I, for interest, read some of source code of Python launcher, and found it used string comparison function (`wcscmp()`, in function `compare_pythons()`) to sort Python version in descending order.

It works well currently. But if Python 3.10 or Python 3.xx comes up in the future, Python 3.xx will be ranked after 3.x.

I modified the Registry and made a fake version Python 3.10, to check the launcher's behaviour.

```
PS > py -0p
Installed Pythons found by C:\Windows\py.exe Launcher for Windows
 -3.8-64        D:\Program Files\Python38\python.exe *
 -3.7-64        D:\Program Files\Python37\python.exe
 -3.7-32        D:\Program Files (x86)\Python37-32\python.exe
 -3.6-32        C:\Program Files (x86)\Python36-32\python.exe
 -3.10-64       D:\Program Files\Python37\python.exe
 -2.7-64        C:\python27-x64\python.exe
```

The result turned out that Python 3.10 was really ranked after 3.x.

And it seems that Python 3.xx should be a valid (or supported) version according to the comment from function `validate_version()`.


```
static BOOL
validate_version(wchar_t * p)
{
    /*
    Version information should start with the major version,
    Optionally followed by a period and a minor version,
    Optionally followed by a minus and one of 32 or 64.
    Valid examples:
      ...
      2.7-32
      The intent is to add to the valid patterns:
      3.10
      3-32
      ...
    */

I am not sure whether this is a potential defect that had been confirmed before... But I do not see some relevant comments in the source code.

----------
components: Windows
messages: 354843
nosy: paul.moore, steve.dower, tim.golden, ynyyn, zach.ware
priority: normal
severity: normal
status: open
title: Launcher for Windows (py.exe) may rank Python 3.xx (in the future) after 3.x
type: behavior
versions: Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38506>
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