Get rid of which dependency in system_which

[sedrubal]

Issue description

In many minimal system installations (container distributions, etc., see #2277) the non-standard command which is not available by default. But pipenv currently requires this in order to find python and other tools. One could say, that this is a packager fail, but I think, the requirements for pipenv should be minimal and there are many other ways to find executables apart from which.

Expected result

pipenv should work in most plank standard container images out of the box.

Actual result

Pipenv fails and you have to specify the python executable with --python argument.

Steps to replicate

$ docker run --rm -it fedora:28 bash
# dnf install pipenv
# pipenv --three
Warning: the which -a system utility is required for Pipenv to find Python installations properly.
  Please install it.
Warning: the which -a system utility is required for Pipenv to find Python installations properly.
  Please install it.
Warning: the which -a system utility is required for Pipenv to find Python installations properly.
  Please install it.
Warning: Python 3 was not found on your system…
You can specify specific versions of Python with:
  $ pipenv --python path/to/python
When possible, provide the verbose output (`--verbose`), especially for locking and dependencies resolving issues.

Ideas to solve it

• I've no idea how what we can do on windows. For Linux, these few python lines do more or less the same as which:

def _which(command: str):
      def is_exe(fpath):
          return os.path.isfile(fpath) and os.access(fpath, os.X_OK)

      fpath, _fname = os.path.split(command)
      if fpath:
          if is_exe(command):
              return command
      else:
          for path in os.environ["PATH"].split(os.pathsep):
              exe_file = os.path.join(path, command)
              if is_exe(exe_file):
                  return exe_file

      return None

• Apart from which, command -v is more standard and available in most shells
• When --three is given and sys.version_info.major == 3, you could just use sys.executable. The same applies for --two and so on.

---

$ pipenv --support

This is from a `fedora:29` beta docker image, as pipenv in `fedora:28` has no `--support` argument. The same issue is present on fedora 29 as well.

Pipenv version: '2018.7.1'

Pipenv location: '/usr/lib/python3.7/site-packages/pipenv'

Python location: '/usr/bin/python3'

Other Python installations in PATH:

Warning: the which -a system utility is required for Pipenv to find Python installations properly.
Please install it.
[...]
PEP 508 Information:

{'implementation_name': 'cpython',
 'implementation_version': '3.7.0',
 'os_name': 'posix',
 'platform_machine': 'x86_64',
 'platform_python_implementation': 'CPython',
 'platform_release': '4.18.7-300.fc29.x86_64',
 'platform_system': 'Linux',
 'platform_version': '#1 SMP Mon Sep 10 15:37:17 UTC 2018',
 'python_full_version': '3.7.0',
 'python_version': '3.7',
 'sys_platform': 'linux'}

System environment variables:

• LANG
• HOSTNAME
• PWD
• HOME
• FBR
• DISTTAG
• FGC
• TERM
• SHLVL
• PATH
• _
• PYTHONDONTWRITEBYTECODE
• PIP_PYTHON_PATH

Pipenv–specific environment variables:

Debug–specific environment variables:

• PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
• LANG: en_US.UTF-8
• PWD: /

---

Contents of Pipfile ('/Pipfile'):

[techalchemy]

I agree that we shouldn't use which, but we actually have a reimplementation of this in pythonfinder which we maintain separately and simply haven't implemented yet (example below).

For the second element:

When --three is given and sys.version_info.major == 3, you could just use sys.executable

It's not quite this simple just because when the user has multiple versions of python 3, we prefer the highest stable release (and I think this is actually implemented using pythonfinder already).

import pythonfinder
finder = pythonfinder.Finder(allow_global=True, system=False)  # allow global searching, use system python i.e. sys.executable
command_path = finder.which("some_command")

You should probably verify that this is actually how it works, I am going to cut a release of pythonfinder soon so it'd be good to double check :)

Would absolutely accept a PR on this though, because yeah, definitely agree that the current approach isn't the best

[uranusjr]

I didn’t check PythonFinder’s implementation, but the implementation provided in the top post does not work on all platforms. Windows, for example, allows you to omit extensions listed in PATHEXT, so python.exe would show up in where python results. I believe there are other platforms with similar behaviours (e.g. Mac OS 9), but they are likely obscure enough we can ignore them for now.

[techalchemy]

(That was why I mentioned the pythonfinder implementation, which doesn't use the code from the original recommendation but instead uses an OS and platform agnostic approach)

[immerrr]

Some inspiration could be borrowed from shutil.which function that's part of Py3 standard library, although some bugs are still open against it.

[uranusjr]

Also (I learnt this only during last week) there is a backport for shutil.which. https://pypi.org/project/whichcraft/

[techalchemy]

this isn't the first time someone mentioned shutil.which, but there are plenty of reasons why we don't use it.

[sedrubal]

Oh I didn't know shutil.which. Can you tell me the reasons not to use it? Is there a related issue?

[uranusjr]

@sedrubal Many of the CPython issues linked by @immerrr are very critical for Pipenv, especially those about Windows.

[Eelviny]

I'm encountering this warning when using the new AWS Lambda distributable for Python.
This is a container runtime so I'm using pipenv install within a Dockerfile.
As I'm already explicitly specifying the version I don't have issues but these new container runtimes don't contain which.

[abbasegbeyemi]

Encountering the same problem here as well. What's the solution?

[oz123]

This should be solved as we no longer use which from vistir or the pipenv which. shutil.which is now used.
Feel free to re-open if you still encounter this issue.