Drop the pyvenv script

[brettcannon]

BPO	25154
Nosy	@warsaw, @brettcannon, @doko42, @pitrou, @scoder, @ericvsmith, @ezio-melotti
Files	issue25154.diff issue25154-1.diff

^{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/brettcannon'
closed_at = <Date 2015-10-27.00:11:39.712>
created_at = <Date 2015-09-17.18:35:21.344>
labels = ['type-bug', 'expert-installation']
title = 'Drop the pyvenv script'
updated_at = <Date 2015-10-27.00:11:39.684>
user = 'https://github.com/brettcannon'

bugs.python.org fields:

activity = <Date 2015-10-27.00:11:39.684>
actor = 'brett.cannon'
assignee = 'brett.cannon'
closed = True
closed_date = <Date 2015-10-27.00:11:39.712>
closer = 'brett.cannon'
components = ['Installation']
creation = <Date 2015-09-17.18:35:21.344>
creator = 'brett.cannon'
dependencies = []
files = ['40579', '40861']
hgrepos = []
issue_num = 25154
keywords = ['patch']
message_count = 18.0
messages = ['250910', '250912', '250920', '250923', '251021', '251457', '251543', '251605', '253102', '253185', '253263', '253264', '253385', '253386', '253444', '253445', '253457', '253508']
nosy_count = 10.0
nosy_names = ['barry', 'brett.cannon', 'doko', 'pitrou', 'scoder', 'eric.smith', 'ezio.melotti', 'python-dev', 'rpointel', 'lac']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25154'
versions = ['Python 3.5', 'Python 3.6']

[brettcannon]

I propose that the pyvenv script be deprecated in Python 3.5 and removed in Python 3.8. The reason for this proposal is because it is non-obvious what version of Python a pyvenv command is tied to (heck, it isn't necessarily obvious that it's Python 3). There would be no loss in functionality since the exact same functionality is available through python3 -m venv. This is a backwards-compatibility change, hence the deprecation, but changing various shell scripts and such should be trivial thanks to the -m flag. This would also help promote the use of -m, especially for any projects that rely on being tied to a specific installed interpreter.

As pointed out in issue bpo-25152, virtualenv provides a -p flag to specify what version of Python should be used to create a virtual environment: https://virtualenv.pypa.io/en/latest/reference.html#virtualenv-command. The pyvenv script and venv package provide no such mechanism since it is included in the stdlib, which makes sense since improvements will be tied to the stdlib of the Python interpreter being used while virtualenv is a standalone project/app.

Some may argue that worrying about this is unnecessary, but we are already ending up with OSs that come with multiple versions of Python pre-installed, let alone when people install their own versions of Python on top of the system installation. For instance, OS X Yosemite comes with Python 2.6 and 2.7, and then if you install the latest version of Python independently you end up with 3 installations. If they all happened to have a pyvenv script you wouldn't easily know which Python interpreter the pyvenv command was going to use for the virtual environment.

Since the pyvenv script is just a script, the deprecation will be in the form of a message printed to sys.stderr in the Tools/scripts/pyvenv file mentioning that the deprecation and that people should switch to python3 -m venv instead. The long deprecation cycle is for those who have pyvenv provided by their OS and only upgrade Python every few years, and thus run the risk of missing the deprecation warning. As for the deprecation in Python 3.5.1, that's to get the warning out immediately and to minimize people missing the deprecation prior to the removal.

[warsaw]

I'm sympathetic, given that in Debian/Ubuntu (and maybe other distros) where we have both Python 3.4 and 3.5, we have to install /usr/bin/pyvenv-3.4 and pyvenv-3.5, and then use symlinks to provide the default version.

[lac]

Due to debian policy decision
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=732703

neither pyenv nor python -m venv

may work for you.

While things are getting changed, it would be good if people running into
this problem got a better error message than:

Error: Command '['<directory>/bin/python3.4', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1

such as 'Your python may not be configured with ensure-pip'

[brettcannon]

the ensurepip case is another issue, so if you want you can file a separate issue for it so it doesn't get lost.

[warsaw]

I have a patch which will at least improve the error message when python3 -m venv fails because python3-venv isn't installed on Debian/Ubuntu. I will work with Doko on this.

[brettcannon]

python-dev did not seem to object to the idea.

[rpointel]

I would prefer to keep this script with the version referring to the version of python used (pyvenv-3.4, pyvenv-3.5, ...).

[brettcannon]

Here is a patch that adds a message to stderr about the deprecation.

[python-dev]

New changeset 6ab285820db2 by Brett Cannon in branch 'default':
Issue bpo-25154: Deprecate the pyvenv script.
https://hg.python.org/cpython/rev/6ab285820db2

[brettcannon]

I have a typo in my commit where I accidentally placed the file argument in str.format() instead of for print() (pointed out on GitHub).