Interpreter lookup fails on Arch Linux

[rpigott]

When trying to create a virtualenv, I get the following result:

$ virtualenv -p python2.7 tmp -vvv --with-traceback
44 setup logging to NOTSET [DEBUG report:43]
59 find interpreter for spec PythonSpec(implementation=CPython, major=2, minor=7) [INFO builtin:62]
59 proposed PythonInfo(spec=CPython3.9.6.final.0-64, exe=/usr/bin/python, platform=linux, version='3.9.6 (default, Jun 30 2021, 10:22:16) \n[GCC 11.1.0]', encoding_fs_io=utf-8-utf-8) [INFO builtin:69]
59 discover PATH[0]=/home/ronan/.local/bin [DEBUG builtin:114]
59 filesystem is case-sensitive [DEBUG info:28]
60 discover PATH[1]=/usr/local/sbin [DEBUG builtin:114]
60 discover PATH[2]=/usr/local/bin [DEBUG builtin:114]
60 discover PATH[3]=/usr/bin [DEBUG builtin:114]
60 discover PATH[4]=/var/lib/flatpak/exports/bin [DEBUG builtin:114]
60 discover PATH[5]=/usr/lib/jvm/default/bin [DEBUG builtin:114]
60 discover PATH[6]=/usr/bin/site_perl [DEBUG builtin:114]
60 discover PATH[7]=/usr/bin/vendor_perl [DEBUG builtin:114]
61 discover PATH[8]=/usr/bin/core_perl [DEBUG builtin:114]
Traceback (most recent call last):
  File "/usr/bin/virtualenv", line 33, in <module>
    sys.exit(load_entry_point('virtualenv==20.7.0', 'console_scripts', 'virtualenv')())
  File "/usr/lib/python3.9/site-packages/virtualenv/__main__.py", line 65, in run_with_catch
    run(args, options, env)
  File "/usr/lib/python3.9/site-packages/virtualenv/__main__.py", line 18, in run
    session = cli_run(args, options, env)
  File "/usr/lib/python3.9/site-packages/virtualenv/run/__init__.py", line 30, in cli_run
    of_session = session_via_cli(args, options, setup_logging, env)
  File "/usr/lib/python3.9/site-packages/virtualenv/run/__init__.py", line 48, in session_via_cli
    parser, elements = build_parser(args, options, setup_logging, env)
  File "/usr/lib/python3.9/site-packages/virtualenv/run/__init__.py", line 72, in build_parser
    raise RuntimeError("failed to find interpreter for {}".format(discover))
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python2.7'

I see something similar has been reported and addressed in #1643/#1910, but distutils is available on my installation and I get the error regardless. Some more info:

$ head -1 /etc/os-release
NAME="Arch Linux"
$ pacman -Qo python virtualenv
/usr/bin/python is owned by python 3.9.6-1
/usr/bin/virtualenv is owned by python-virtualenv 20.7.0-1
$ python -c 'import disutils; print(distutils.__file__)' | pacman -Qo -
/usr/lib/python3.9/distutils/__init__.py is owned by python 3.9.6-1

The behavior is the same for every python version I tested, with the exception of 3.9.6 which the only version installed on my machine.

[gaborbernat]

As detailed by https://virtualenv.pypa.io/en/latest/user_guide.html#creators virtualenv out of the box is only able to create virtual environments for python versions that are already installed globally on your OS. So it's working as expected. If you'd like to create python2.7 environment you need to install first python27