Revert "get-poetry.py fallback to standard executables (#1878) (#2426)"

This reverts commit f812822.

README.md

@@ -23,13 +23,6 @@ curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poet
 
 Alternatively, you can download the `get-poetry.py` file and execute it separately.
 
-The setup script must be able to find one of following executables in your shell's path environment:
-
-- `python` (which can be a py3 or py2 interpreter)
-- `python3`
-- `py.exe -3` (Windows)
-- `py.exe -2` (Windows)
-
 If you want to install prerelease versions, you can do so by passing `--preview` to `get-poetry.py`:
 
 ```bash

get-poetry.py

@@ -197,7 +197,8 @@ def expanduser(path):
 POETRY_LIB_BACKUP = os.path.join(POETRY_HOME, "lib-backup")
 
 
-BIN = """# -*- coding: utf-8 -*-
+BIN = """#!/usr/bin/env python
+# -*- coding: utf-8 -*-
 import glob
 import sys
 import os
@@ -216,7 +217,7 @@ def expanduser(path):
     main()
 """
 
-BAT = u('@echo off\r\n{python_executable} "{poetry_bin}" %*\r\n')
+BAT = u('@echo off\r\npython "{poetry_bin}" %*\r\n')
 
 
 PRE_MESSAGE = """# Welcome to {poetry}!
@@ -588,61 +589,23 @@ def _make_lib(self, version):
             finally:
                 gz.close()
 
-    def _which_python(self):
-        """Decides which python executable we'll embed in the launcher script."""
-        allowed_executables = ["python", "python3"]
-        if WINDOWS:
-            allowed_executables += ["py.exe -3", "py.exe -2"]
-
-        # \d in regex ensures we can convert to int later
-        version_matcher = re.compile(r"^Python (?P<major>\d+)\.(?P<minor>\d+)\..+$")
-        fallback = None
-        for executable in allowed_executables:
-            try:
-                raw_version = subprocess.check_output(
-                    executable + " --version", stderr=subprocess.STDOUT, shell=True
-                ).decode("utf-8")
-            except subprocess.CalledProcessError:
-                continue
-
-            match = version_matcher.match(raw_version.strip())
-            if match and tuple(map(int, match.groups())) >= (3, 0):
-                # favor the first py3 executable we can find.
-                return executable
-            if fallback is None:
-                # keep this one as the fallback; it was the first valid executable we found.
-                fallback = executable
-
-        if fallback is None:
-            raise RuntimeError(
-                "No python executable found in shell environment. Tried: "
-                + str(allowed_executables)
-            )
-
-        return fallback
-
     def make_bin(self):
         if not os.path.exists(POETRY_BIN):
             os.mkdir(POETRY_BIN, 0o755)
 
-        python_executable = self._which_python()
-
         if WINDOWS:
             with open(os.path.join(POETRY_BIN, "poetry.bat"), "w") as f:
                 f.write(
                     u(
                         BAT.format(
-                            python_executable=python_executable,
                             poetry_bin=os.path.join(POETRY_BIN, "poetry").replace(
                                 os.environ["USERPROFILE"], "%USERPROFILE%"
-                            ),
+                            )
                         )
                     )
                 )
 
         with open(os.path.join(POETRY_BIN, "poetry"), "w", encoding="utf-8") as f:
-            if not WINDOWS:
-                f.write(u("#!/usr/bin/env {}\n".format(python_executable)))
             f.write(u(BIN))
 
         if not WINDOWS: