Get rid of which dependency in system_which

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’):

[abbasegbeyemi]

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

[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.