Allow py launcher to launch other registered Pythons

[petsutergmailcom]

BPO	32730
Nosy	@pfmoore, @tjguk, @zware, @zooba, @uranusjr

^{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 2018-01-31.15:57:13.659>
labels = ['3.8', 'type-feature', '3.7', 'OS-windows']
title = 'Allow py launcher to launch other registered Pythons'
updated_at = <Date 2019-12-12.18:09:32.460>
user = 'https://bugs.python.org/petsutergmailcom'

bugs.python.org fields:

activity = <Date 2019-12-12.18:09:32.460>
actor = 'uranusjr'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Windows']
creation = <Date 2018-01-31.15:57:13.659>
creator = 'petsuter@gmail.com'
dependencies = []
files = []
hgrepos = []
issue_num = 32730
keywords = []
message_count = 3.0
messages = ['311338', '311378', '313188']
nosy_count = 6.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'uranusjr', 'petsuter@gmail.com']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32730'
versions = ['Python 2.7', 'Python 3.6', 'Python 3.7', 'Python 3.8']

[petsutergmailcom]

For example Anaconda Python is registered under HKEY_LOCAL_MACHINE\Software\Python\ContinuumAnalytics\Anaconda36-64\ as described in PEP-514 "Python registration in the Windows registry" .

The py launcher from PEP-397 however ignores that and only considers HKEY_LOCAL_MACHINE\Software\Python\PythonCore\ registrations.

There seems to be no mechanism to register Anaconda Python with the py launcher. Anaconda considers this a bug in the Python launcher. ContinuumIO/anaconda-issues#149 (comment)

Shouldn't this be possible? Maybe via py.ini [defaults]?

[zooba]

Yep, this was part of the plan. Just hasn't happened yet (it probably requires a significant rewrite of the launcher which nobody has volunteered to do or found the time for).

I thought I had another open bug on this too... if someone finds it, feel free to dup this one.

[zooba]

Since I took the time to do a brain dump of my thinking here, feel free to review/contribute to https://github.com/zooba/PyLauncher/wiki

Note that the code in that repo doesn't match the wiki page, and while I think it's good code I do now think it's the wrong approach. So ignore that and just read the "spec"

[petsuter]

Has this now happened in https://docs.python.org/3/whatsnew/3.11.html#windows-py-exe-launcher-improvements?

[petsuter]

Nice, it seems to work!

$ py -0
 -V:3.11 *        Python 3.11 (64-bit)
 -V:3.10          Python 3.10 (64-bit)
 -V:3.8           Python 3.8 (64-bit)
 -V:3.7           Python 3.7 (64-bit)
 -V:2.7
 -V:ContinuumAnalytics/Anaconda39-64 Anaconda py39_4.12.0

$ py -3.9 --version
No suitable Python runtime found

$ py -V:Anaconda --version
Python 3.9.12