Windows launcher version lookup flawed

[LarryZA]

BPO	34142
Nosy	@pfmoore, @tjguk, @zware, @eryksun, @zooba

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2018-07-18.02:09:34.963>
labels = ['3.8', '3.9', '3.10', 'type-feature', 'OS-windows', 'docs']
title = 'Windows launcher version lookup flawed'
updated_at = <Date 2021-03-27.04:50:19.776>
user = 'https://bugs.python.org/LarryZA'

bugs.python.org fields:

activity = <Date 2021-03-27.04:50:19.776>
actor = 'eryksun'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation', 'Windows']
creation = <Date 2018-07-18.02:09:34.963>
creator = 'LarryZA'
dependencies = []
files = []
hgrepos = []
issue_num = 34142
keywords = []
message_count = 4.0
messages = ['321855', '321858', '321859', '321861']
nosy_count = 7.0
nosy_names = ['paul.moore', 'tim.golden', 'docs@python', 'zach.ware', 'eryksun', 'steve.dower', 'LarryZA']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue34142'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[LarryZA]

In the manual it says that the following .ini file will cause the launcher to run Python3.1 for calls of py or py -3

[defaults]
python=3
python3=3.1

On my Windows 7 machine I have Python2.7-32, Python3.4-64, and Python3.7-64 (installed in that order).

Setting the ini to:

[defaults]
python=3
python3=3.4

results in py running 3.7-64 (expected 3.4-64) and py -3 running 3.4-64.

Setting both to point to 3.4 in the ini will run 3.4-64 for both commands.

[zooba]

The behavior is correct, so the documentation needs fixing.

Which page has that example on it? Is it assuming that you only have 3.1 installed?

[LarryZA]

https://docs.python.org/3/using/windows.html

Section 3.4.4.2

[eryksun]

This line in the docs is incorrect:

If PY_PYTHON=3 and PY_PYTHON3=3.1, the commands python and python3 
will both use specifically 3.1

It implies that setting the python virtual command to "3" or "2" will use the configured version of the python3 or python2 virtual command. As implemented, these three virtual commands are separately configured.

The python command is different in one way, since it's also the overall default. If the version set for python2 or python3 doesn't match an installed version, that's the end of the search. OTOH, the python command will continue to search for any version. For a shebang it prefers "2" over "3", and vice versa for the REPL or a script without a shebang.