shebanged scripts can escape from venv depending on how it was created

[asottile]

BPO	39656
Nosy	@vsajip, @asottile
PRs	bpo-39656: Ensure bin/python3.# is always present in virtual environments #19030

^{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 = <Date 2020-03-19.11:20:59.876>
created_at = <Date 2020-02-16.19:21:51.580>
labels = ['library', '3.9']
title = 'shebanged scripts can escape from `venv` depending on how it was created'
updated_at = <Date 2020-03-19.11:20:59.875>
user = 'https://github.com/asottile'

bugs.python.org fields:

activity = <Date 2020-03-19.11:20:59.875>
actor = 'vinay.sajip'
assignee = 'none'
closed = True
closed_date = <Date 2020-03-19.11:20:59.876>
closer = 'vinay.sajip'
components = ['Library (Lib)']
creation = <Date 2020-02-16.19:21:51.580>
creator = 'Anthony Sottile'
dependencies = []
files = []
hgrepos = []
issue_num = 39656
keywords = ['patch']
message_count = 2.0
messages = ['362095', '364389']
nosy_count = 2.0
nosy_names = ['vinay.sajip', 'Anthony Sottile']
pr_nums = ['19030']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue39656'
versions = ['Python 3.9']

[asottile]

This is distilled from a larger example to be small/silly, however this caused real problems

A script which was intended for python3.6 exactly was written as follows:

#!/usr/bin/env python3.6
...

when creating a virtualenv with python3.6 -m venv venv36 you end up with python / python3 / python3.6 executables in the venv

however, when creating a virtualenv with python3 -m venv venv36 you only end up with python / python3 executables

---

using -mvirtualenv (pypa/virtualenv) instead of venv, all three are reliably created

---

the fix is fairly straightforward, adding f'python3.{sys.version_info[0]}' to this tuple:

cpython/Lib/venv/__init__.py

Line 246 in c33bdbb

for suffix in ('python', 'python3'):

[vsajip]

New changeset 58ec58a by Anthony Sottile in branch 'master':
bpo-39656: Ensure bin/python3.# is always present in virtual environments on POSIX (GH-19030)
58ec58a