macOS python.org installers only add or modify framework Versions/Current symlink for Python 2.x installs, not Python 3.x

[KevinPackard]

BPO	38329
Nosy	@ronaldoussoren, @ned-deily
PRs	bpo-38329: python.org macOS installers now update Current symlink #19650

^{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 = 'https://github.com/ned-deily'
closed_at = <Date 2020-04-22.08:33:10.583>
created_at = <Date 2019-09-30.19:37:04.712>
labels = ['OS-mac', 'type-bug', 'expert-installation', '3.9']
title = 'macOS python.org installers only add or modify framework Versions/Current symlink for Python 2.x installs, not Python 3.x'
updated_at = <Date 2020-04-22.08:33:10.582>
user = 'https://bugs.python.org/KevinPackard'

bugs.python.org fields:

activity = <Date 2020-04-22.08:33:10.582>
actor = 'ned.deily'
assignee = 'ned.deily'
closed = True
closed_date = <Date 2020-04-22.08:33:10.583>
closer = 'ned.deily'
components = ['Installation', 'macOS']
creation = <Date 2019-09-30.19:37:04.712>
creator = 'KevinPackard'
dependencies = []
files = []
hgrepos = []
issue_num = 38329
keywords = ['patch']
message_count = 4.0
messages = ['353612', '353632', '366993', '366994']
nosy_count = 3.0
nosy_names = ['ronaldoussoren', 'ned.deily', 'KevinPackard']
pr_nums = ['19650']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38329'
versions = ['Python 3.9']

[KevinPackard]

The macOS installer for Python 3.7.4 places "Python.framework" into /Library/Frameworks/ However, the top-level symlinks inside the framework are broken for "Headers" and "Resources". Because of this, the framework can not be imported into an Xcode project.

[ned-deily]

Thanks for the reminder. Unfortunately, the macOS installer is working as designed. As discussed at length in bpo-18117 (and elsewhere), building using the -framework Python, either directly in compiler calls or indirectly through Xcode is problematic because python.org Python installers install all versions, 2.x and 3.x, into the same framework location, /Library/Frameworks/Python.framework. Since it was common especially in the early days of Python 3 to install both Python 2 and Python 3, the decision was made to only have Python 2.x installs add or modify the Current symlink. As also noted, it was probably a mistake back then to not install Python 3.x versions to a differently-names framework so you can be sure whether you are attempting to link with Python 2 or Python 3 but that ship has sailed. However now that Python 2 is about to enter end-of-life, we should reconsider that behavior.

In the meantime, there should be a simple workaround: just create the symlink yourself after installing a new Python 3.x version. So something like:

sudo sh
umask 022
cd /Library/Frameworks/Python.framework/Versions
rm -f Current
ln -s 3.7 Current
exit

[ned-deily]

New changeset bcc136b by Ned Deily in branch 'master':
bpo-38329: python.org macOS installers now update Current symlink (GH-19650)
bcc136b

[ned-deily]

With Python 2 now officially retired, it's time to change the installer behavior. With the merged change, as of Python 3.9.0 (alpha 6) the python.org macOS installers will now update the Current version symmlink in the /Library/Frameworks Python being installed. Since this would be a change in behavior that could affect current users of Python 3.8.x or 3.7.x, I think we should not backport this to those versions. Thanks again for the report!