Returns the path the system-wide python binary.
        (In case we're running in a virtualenv or venv)

def _get_system_python_executable():
    """ Returns the path the system-wide python binary.
        (In case we're running in a virtualenv or venv)
    """
    # This function is required by get_package_as_folder() to work
    # inside a virtualenv, since venv creation will fail with
    # the virtualenv's local python binary.
    # (venv/virtualenv incompatibility)

    # Abort if not in virtualenv or venv:
    if not hasattr(sys, "real_prefix") and (
            not hasattr(sys, "base_prefix") or
            os.path.normpath(sys.base_prefix) ==
            os.path.normpath(sys.prefix)):
        return sys.executable

    # Extract prefix we need to look in:
    if hasattr(sys, "real_prefix"):
        search_prefix = sys.real_prefix  # virtualenv
    else:
        search_prefix = sys.base_prefix  # venv

    def python_binary_from_folder(path):
        def binary_is_usable(python_bin):
            try:
                filenotfounderror = FileNotFoundError
            except NameError:  # Python 2
                filenotfounderror = OSError
            try:
                subprocess.check_output([
                    os.path.join(path, python_bin), "--version"
                ], stderr=subprocess.STDOUT)
                return True
            except (subprocess.CalledProcessError, filenotfounderror):
                return False

        python_name = "python" + sys.version
        while (not binary_is_usable(python_name) and
               python_name.find(".") > 0):
            # Try less specific binary name:
            python_name = python_name.rpartition(".")[0]
        if binary_is_usable(python_name):
            return os.path.join(path, python_name)
        return None

    # Return from sys.real_prefix if present:
    result = python_binary_from_folder(search_prefix)
    if result is not None:
        return result

    # Check out all paths in $PATH:
    bad_candidates = []
    good_candidates = []
    ever_had_nonvenv_path = False
    for p in os.environ.get("PATH", "").split(":"):
        # Skip if not possibly the real system python:
        if not os.path.normpath(p).startswith(
                os.path.normpath(search_prefix)
                ):
            continue

        # First folders might be virtualenv/venv we want to avoid:
        if not ever_had_nonvenv_path:
            sep = os.path.sep
            if ("system32" not in p.lower() and "usr" not in p) or \
                    {"home", ".tox"}.intersection(set(p.split(sep))) or \
                    "users" in p.lower():
                # Doesn't look like bog-standard system path.
                if (p.endswith(os.path.sep + "bin") or
                        p.endswith(os.path.sep + "bin" + os.path.sep)):
                    # Also ends in "bin" -> likely virtualenv/venv.
                    # Add as unfavorable / end of candidates:
                    bad_candidates.append(p)
                    continue
            ever_had_nonvenv_path = True

        good_candidates.append(p)

    # See if we can now actually find the system python:
    for p in good_candidates + bad_candidates:
        result = python_binary_from_folder(p)
        if result is not None:
            return result

    raise RuntimeError("failed to locate system python in: " +
                       sys.real_prefix)