Method from_env

pex/interpreter.py:1187–1227

Resolve a PythonInterpreter as /usr/bin/env would. :param hashbang: A string, e.g. "python3.3" representing some binary on the search path. :param paths: The search path to use; defaults to $PATH. :return: the first matching interpreter found or `None`.

(
        cls,
        hashbang,  # type: str
        paths=None,  # type: Optional[Iterable[str]]
    )

    @classmethod
    def from_env(
        cls,
        hashbang,  # type: str
        paths=None,  # type: Optional[Iterable[str]]
    ):
        # type: (...) -> Optional[PythonInterpreter]
        """Resolve a PythonInterpreter as /usr/bin/env would.

        :param hashbang: A string, e.g. "python3.3" representing some binary on the search path.
        :param paths: The search path to use; defaults to $PATH.
        :return: the first matching interpreter found or `None`.
        """

        def hashbang_matches(fn):
            basefile = os.path.basename(fn)
            return hashbang == basefile

        for interpreter in cls._identify_interpreters(
            filter=hashbang_matches, error_handler=None, paths=paths
        ):
            return interpreter

        if WINDOWS and hashbang.startswith("python"):
            # See: https://docs.python.org/3/using/windows.html#launcher
            env = os.environ.copy()
            env["PYLAUNCHER_DRYRUN"] = "1"

            args = ["py"]
            version_part = hashbang[len("python") :]
            if version_part:
                args.append("-{version}".format(version=version_part))

            with open(os.devnull, "wb") as fp:
                process = subprocess.Popen(args=args, env=env, stdout=subprocess.PIPE, stderr=fp)
                stdout, _ = process.communicate()
                if process.returncode == 0:
                    # Windows is only supported for Python 3; so this cast is safe:
                    result = cast(str, stdout.decode("utf-8").strip())
                    return cls.from_binary(result)

        return None

    @classmethod
    def _spawn_from_binary(