sysconfig.py

"""Access to Python's configuration information."""

import os
import sys
from os.path import pardir, realpath

__all__ = [
    'get_config_h_filename',
    'get_config_var',
    'get_config_vars',
    'get_makefile_filename',
    'get_path',
    'get_path_names',
    'get_paths',
    'get_platform',
    'get_python_version',
    'get_scheme_names',
    'parse_config_h',
]

# Keys for get_config_var() that are never converted to Python integers.
_ALWAYS_STR = {
    'MACOSX_DEPLOYMENT_TARGET',
}

_INSTALL_SCHEMES = {
    'posix_prefix': {
        'stdlib': '{installed_base}/{platlibdir}/python{py_version_short}',
        'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}',
        'purelib': '{base}/lib/python{py_version_short}/site-packages',
        'platlib': '{platbase}/{platlibdir}/python{py_version_short}/site-packages',
        'include':
            '{installed_base}/include/python{py_version_short}{abiflags}',
        'platinclude':
            '{installed_platbase}/include/python{py_version_short}{abiflags}',
        'scripts': '{base}/bin',
        'data': '{base}',
        },
    'posix_home': {
        'stdlib': '{installed_base}/lib/python',
        'platstdlib': '{base}/lib/python',
        'purelib': '{base}/lib/python',
        'platlib': '{base}/lib/python',
        'include': '{installed_base}/include/python',
        'platinclude': '{installed_base}/include/python',
        'scripts': '{base}/bin',
        'data': '{base}',
        },
    'nt': {
        'stdlib': '{installed_base}/Lib',
        'platstdlib': '{base}/Lib',
        'purelib': '{base}/Lib/site-packages',
        'platlib': '{base}/Lib/site-packages',
        'include': '{installed_base}/Include',
        'platinclude': '{installed_base}/Include',
        'scripts': '{base}/Scripts',
        'data': '{base}',
        },
    }

# backup the original posix_prefix as rpm_prefix
# RPM packages use it and we need to be able to read it even when changed
_INSTALL_SCHEMES['rpm_prefix'] = _INSTALL_SCHEMES['posix_prefix']
# Virtualenv >= 20.10.0 favors the "venv" scheme over the defaults when creating virtual environments.
# See: https://github.com/pypa/virtualenv/commit/8da79db86d8a5c74d03667a40e64ff832076445e
# See: https://bugs.python.org/issue45413
# "venv" should be the same as the unpatched posix_prefix for us,
# so new virtual environments aren't created with paths like venv/local/bin/python.
_INSTALL_SCHEMES['venv'] = _INSTALL_SCHEMES['posix_prefix']

if (not (hasattr(sys, 'real_prefix') or
    sys.prefix != sys.base_prefix) and
    'RPM_BUILD_ROOT' not in os.environ):
        _INSTALL_SCHEMES['posix_prefix'] = {
            'stdlib': '{installed_base}/{platlibdir}/python{py_version_short}',
            'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}',
            'purelib': '{base}/local/lib/python{py_version_short}/site-packages',
            'platlib': '{platbase}/local/{platlibdir}/python{py_version_short}/site-packages',
            'include':
                '{installed_base}/include/python{py_version_short}{abiflags}',
            'platinclude':
                '{installed_platbase}/include/python{py_version_short}{abiflags}',
            'scripts': '{base}/local/bin',
            'data': '{base}/local',
        }

# NOTE: site.py has copy of this function.
# Sync it when modify this function.
def _getuserbase():
    env_base = os.environ.get("PYTHONUSERBASE", None)
    if env_base:
        return env_base

    # VxWorks has no home directories
    if sys.platform == "vxworks":
        return None

    def joinuser(*args):
        return os.path.expanduser(os.path.join(*args))

    if os.name == "nt":
        base = os.environ.get("APPDATA") or "~"
        return joinuser(base, "Python")

    if sys.platform == "darwin" and sys._framework:
        return joinuser("~", "Library", sys._framework,
                        f"{sys.version_info[0]}.{sys.version_info[1]}")

    return joinuser("~", ".local")

_HAS_USER_BASE = (_getuserbase() is not None)

if _HAS_USER_BASE:
    _INSTALL_SCHEMES |= {
        # NOTE: When modifying "purelib" scheme, update site._get_path() too.
        'nt_user': {
            'stdlib': '{userbase}/Python{py_version_nodot_plat}',
            'platstdlib': '{userbase}/Python{py_version_nodot_plat}',
            'purelib': '{userbase}/Python{py_version_nodot_plat}/site-packages',
            'platlib': '{userbase}/Python{py_version_nodot_plat}/site-packages',
            'include': '{userbase}/Python{py_version_nodot_plat}/Include',
            'scripts': '{userbase}/Python{py_version_nodot_plat}/Scripts',
            'data': '{userbase}',
            },
        'posix_user': {
            'stdlib': '{userbase}/{platlibdir}/python{py_version_short}',
            'platstdlib': '{userbase}/{platlibdir}/python{py_version_short}',
            'purelib': '{userbase}/lib/python{py_version_short}/site-packages',
            'platlib': '{userbase}/lib/python{py_version_short}/site-packages',
            'include': '{userbase}/include/python{py_version_short}',
            'scripts': '{userbase}/bin',
            'data': '{userbase}',
            },
        'osx_framework_user': {
            'stdlib': '{userbase}/lib/python',
            'platstdlib': '{userbase}/lib/python',
            'purelib': '{userbase}/lib/python/site-packages',
            'platlib': '{userbase}/lib/python/site-packages',
            'include': '{userbase}/include/python{py_version_short}',
            'scripts': '{userbase}/bin',
            'data': '{userbase}',
            },
    }

_SCHEME_KEYS = ('stdlib', 'platstdlib', 'purelib', 'platlib', 'include',
                'scripts', 'data')

_PY_VERSION = sys.version.split()[0]
_PY_VERSION_SHORT = f'{sys.version_info[0]}.{sys.version_info[1]}'
_PY_VERSION_SHORT_NO_DOT = f'{sys.version_info[0]}{sys.version_info[1]}'
_PREFIX = os.path.normpath(sys.prefix)
_BASE_PREFIX = os.path.normpath(sys.base_prefix)
_EXEC_PREFIX = os.path.normpath(sys.exec_prefix)
_BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix)
_CONFIG_VARS = None
_USER_BASE = None

# Regexes needed for parsing Makefile (and similar syntaxes,
# like old-style Setup files).
_variable_rx = r"([a-zA-Z][a-zA-Z0-9_]+)\s*=\s*(.*)"
_findvar1_rx = r"\$\(([A-Za-z][A-Za-z0-9_]*)\)"
_findvar2_rx = r"\${([A-Za-z][A-Za-z0-9_]*)}"


def _safe_realpath(path):
    try:
        return realpath(path)
    except OSError:
        return path

if sys.executable:
    _PROJECT_BASE = os.path.dirname(_safe_realpath(sys.executable))
else:
    # sys.executable can be empty if argv[0] has been changed and Python is
    # unable to retrieve the real program name
    _PROJECT_BASE = _safe_realpath(os.getcwd())

if (os.name == 'nt' and
    _PROJECT_BASE.lower().endswith(('\\pcbuild\\win32', '\\pcbuild\\amd64'))):
    _PROJECT_BASE = _safe_realpath(os.path.join(_PROJECT_BASE, pardir, pardir))

# set for cross builds
if "_PYTHON_PROJECT_BASE" in os.environ:
    _PROJECT_BASE = _safe_realpath(os.environ["_PYTHON_PROJECT_BASE"])

def _is_python_source_dir(d):
    for fn in ("Setup", "Setup.local"):
        if os.path.isfile(os.path.join(d, "Modules", fn)):
            return True
    return False

_sys_home = getattr(sys, '_home', None)

if os.name == 'nt':
    def _fix_pcbuild(d):
        if d and os.path.normcase(d).startswith(
                os.path.normcase(os.path.join(_PREFIX, "PCbuild"))):
            return _PREFIX
        return d
    _PROJECT_BASE = _fix_pcbuild(_PROJECT_BASE)
    _sys_home = _fix_pcbuild(_sys_home)

def is_python_build(check_home=False):
    if check_home and _sys_home:
        return _is_python_source_dir(_sys_home)
    return _is_python_source_dir(_PROJECT_BASE)

_PYTHON_BUILD = is_python_build(True)

if _PYTHON_BUILD:
    for scheme in ('posix_prefix', 'posix_home'):
        # On POSIX-y platforms, Python will:
        # - Build from .h files in 'headers' (which is only added to the
        #   scheme when building CPython)
        # - Install .h files to 'include'
        scheme = _INSTALL_SCHEMES[scheme]
        scheme['headers'] = scheme['include']
        scheme['include'] = '{srcdir}/Include'
        scheme['platinclude'] = '{projectbase}/.'


def _subst_vars(s, local_vars):
    try:
        return s.format(**local_vars)
    except KeyError as var:
        try:
            return s.format(**os.environ)
        except KeyError:
            raise AttributeError(f'{var}') from None

def _extend_dict(target_dict, other_dict):
    target_keys = target_dict.keys()
    for key, value in other_dict.items():
        if key in target_keys:
            continue
        target_dict[key] = value


def _expand_vars(scheme, vars):
    res = {}
    if vars is None:
        vars = {}
    _extend_dict(vars, get_config_vars())

    for key, value in _INSTALL_SCHEMES[scheme].items():
        if os.name in ('posix', 'nt'):
            value = os.path.expanduser(value)
        res[key] = os.path.normpath(_subst_vars(value, vars))
    return res


def _get_preferred_schemes():
    if os.name == 'nt':
        return {
            'prefix': 'nt',
            'home': 'posix_home',
            'user': 'nt_user',
        }
    if sys.platform == 'darwin' and sys._framework:
        return {
            'prefix': 'posix_prefix',
            'home': 'posix_home',
            'user': 'osx_framework_user',
        }
    return {
        'prefix': 'posix_prefix',
        'home': 'posix_home',
        'user': 'posix_user',
    }


def get_preferred_scheme(key):
    scheme = _get_preferred_schemes()[key]
    if scheme not in _INSTALL_SCHEMES:
        raise ValueError(
            f"{key!r} returned {scheme!r}, which is not a valid scheme "
            f"on this platform"
        )
    return scheme


def get_default_scheme():
    return get_preferred_scheme('prefix')


def _parse_makefile(filename, vars=None, keep_unresolved=True):
    """Parse a Makefile-style file.

    A dictionary containing name/value pairs is returned.  If an
    optional dictionary is passed in as the second argument, it is
    used instead of a new dictionary.
    """
    import re

    if vars is None:
        vars = {}
    done = {}
    notdone = {}

    with open(filename, encoding=sys.getfilesystemencoding(),
              errors="surrogateescape") as f:
        lines = f.readlines()

    for line in lines:
        if line.startswith('#') or line.strip() == '':
            continue
        m = re.match(_variable_rx, line)
        if m:
            n, v = m.group(1, 2)
            v = v.strip()
            # `$$' is a literal `$' in make
            tmpv = v.replace('$$', '')

            if "$" in tmpv:
                notdone[n] = v
            else:
                try:
                    if n in _ALWAYS_STR:
                        raise ValueError

                    v = int(v)
                except ValueError:
                    # insert literal `$'
                    done[n] = v.replace('$$', '$')
                else:
                    done[n] = v

    # do variable interpolation here
    variables = list(notdone.keys())

    # Variables with a 'PY_' prefix in the makefile. These need to
    # be made available without that prefix through sysconfig.
    # Special care is needed to ensure that variable expansion works, even
    # if the expansion uses the name without a prefix.
    renamed_variables = ('CFLAGS', 'LDFLAGS', 'CPPFLAGS')

    while len(variables) > 0:
        for name in tuple(variables):
            value = notdone[name]
            m1 = re.search(_findvar1_rx, value)
            m2 = re.search(_findvar2_rx, value)
            if m1 and m2:
                m = m1 if m1.start() < m2.start() else m2
            else:
                m = m1 if m1 else m2
            if m is not None:
                n = m.group(1)
                found = True
                if n in done:
                    item = str(done[n])
                elif n in notdone:
                    # get it on a subsequent round
                    found = False
                elif n in os.environ:
                    # do it like make: fall back to environment
                    item = os.environ[n]

                elif n in renamed_variables:
                    if (name.startswith('PY_') and
                        name[3:] in renamed_variables):
                        item = ""

                    elif 'PY_' + n in notdone:
                        found = False

                    else:
                        item = str(done['PY_' + n])

                else:
                    done[n] = item = ""

                if found:
                    after = value[m.end():]
                    value = value[:m.start()] + item + after
                    if "$" in after:
                        notdone[name] = value
                    else:
                        try:
                            if name in _ALWAYS_STR:
                                raise ValueError
                            value = int(value)
                        except ValueError:
                            done[name] = value.strip()
                        else:
                            done[name] = value
                        variables.remove(name)

                        if name.startswith('PY_') \
                        and name[3:] in renamed_variables:

                            name = name[3:]
                            if name not in done:
                                done[name] = value

            else:
                # Adds unresolved variables to the done dict.
                # This is disabled when called from distutils.sysconfig
                if keep_unresolved:
                    done[name] = value
                # bogus variable reference (e.g. "prefix=$/opt/python");
                # just drop it since we can't deal
                variables.remove(name)

    # strip spurious spaces
    for k, v in done.items():
        if isinstance(v, str):
            done[k] = v.strip()

    # save the results in the global dictionary
    vars.update(done)
    return vars


def get_makefile_filename():
    """Return the path of the Makefile."""
    if _PYTHON_BUILD:
        return os.path.join(_sys_home or _PROJECT_BASE, "Makefile")
    if hasattr(sys, 'abiflags'):
        config_dir_name = f'config-{_PY_VERSION_SHORT}{sys.abiflags}'
    else:
        config_dir_name = 'config'
    if hasattr(sys.implementation, '_multiarch'):
        config_dir_name += f'-{sys.implementation._multiarch}'
    return os.path.join(get_path('stdlib'), config_dir_name, 'Makefile')


def _get_sysconfigdata_name():
    multiarch = getattr(sys.implementation, '_multiarch', '')
    return os.environ.get(
        '_PYTHON_SYSCONFIGDATA_NAME',
        f'_sysconfigdata_{sys.abiflags}_{sys.platform}_{multiarch}',
    )


def _generate_posix_vars():
    """Generate the Python module containing build-time variables."""
    import pprint
    vars = {}
    # load the installed Makefile:
    makefile = get_makefile_filename()
    try:
        _parse_makefile(makefile, vars)
    except OSError as e:
        msg = f"invalid Python installation: unable to open {makefile}"
        if hasattr(e, "strerror"):
            msg = f"{msg} ({e.strerror})"
        raise OSError(msg)
    # load the installed pyconfig.h:
    config_h = get_config_h_filename()
    try:
        with open(config_h, encoding="utf-8") as f:
            parse_config_h(f, vars)
    except OSError as e:
        msg = f"invalid Python installation: unable to open {config_h}"
        if hasattr(e, "strerror"):
            msg = f"{msg} ({e.strerror})"
        raise OSError(msg)
    # On AIX, there are wrong paths to the linker scripts in the Makefile
    # -- these paths are relative to the Python source, but when installed
    # the scripts are in another directory.
    if _PYTHON_BUILD:
        vars['BLDSHARED'] = vars['LDSHARED']

    # There's a chicken-and-egg situation on OS X with regards to the
    # _sysconfigdata module after the changes introduced by #15298:
    # get_config_vars() is called by get_platform() as part of the
    # `make pybuilddir.txt` target -- which is a precursor to the
    # _sysconfigdata.py module being constructed.  Unfortunately,
    # get_config_vars() eventually calls _init_posix(), which attempts
    # to import _sysconfigdata, which we won't have built yet.  In order
    # for _init_posix() to work, if we're on Darwin, just mock up the
    # _sysconfigdata module manually and populate it with the build vars.
    # This is more than sufficient for ensuring the subsequent call to
    # get_platform() succeeds.
    name = _get_sysconfigdata_name()
    if 'darwin' in sys.platform:
        import types
        module = types.ModuleType(name)
        module.build_time_vars = vars
        sys.modules[name] = module

    pybuilddir = f'build/lib.{get_platform()}-{_PY_VERSION_SHORT}'
    if hasattr(sys, "gettotalrefcount"):
        pybuilddir += '-pydebug'
    os.makedirs(pybuilddir, exist_ok=True)
    destfile = os.path.join(pybuilddir, name + '.py')

    with open(destfile, 'w', encoding='utf8') as f:
        f.write('# system configuration generated and used by'
                ' the sysconfig module\n')
        f.write('build_time_vars = ')
        pprint.pprint(vars, stream=f)

    # Create file used for sys.path fixup -- see Modules/getpath.c
    with open('pybuilddir.txt', 'w', encoding='utf8') as f:
        f.write(pybuilddir)

def _init_posix(vars):
    """Initialize the module as appropriate for POSIX systems."""
    # _sysconfigdata is generated at build time, see _generate_posix_vars()
    name = _get_sysconfigdata_name()
    _temp = __import__(name, globals(), locals(), ['build_time_vars'], 0)
    build_time_vars = _temp.build_time_vars
    vars.update(build_time_vars)

def _init_non_posix(vars):
    """Initialize the module as appropriate for NT"""
    # set basic install directories
    import _imp
    vars['LIBDEST'] = get_path('stdlib')
    vars['BINLIBDEST'] = get_path('platstdlib')
    vars['INCLUDEPY'] = get_path('include')
    vars['EXT_SUFFIX'] = _imp.extension_suffixes()[0]
    vars['EXE'] = '.exe'
    vars['VERSION'] = _PY_VERSION_SHORT_NO_DOT
    vars['BINDIR'] = os.path.dirname(_safe_realpath(sys.executable))
    vars['TZPATH'] = ''

#
# public APIs
#


def parse_config_h(fp, vars=None):
    """Parse a config.h-style file.

    A dictionary containing name/value pairs is returned.  If an
    optional dictionary is passed in as the second argument, it is
    used instead of a new dictionary.
    """
    if vars is None:
        vars = {}
    import re
    define_rx = re.compile("#define ([A-Z][A-Za-z0-9_]+) (.*)\n")
    undef_rx = re.compile("/[*] #undef ([A-Z][A-Za-z0-9_]+) [*]/\n")

    while True:
        line = fp.readline()
        if not line:
            break
        m = define_rx.match(line)
        if m:
            n, v = m.group(1, 2)
            try:
                if n in _ALWAYS_STR:
                    raise ValueError
                v = int(v)
            except ValueError:
                pass
            vars[n] = v
        else:
            m = undef_rx.match(line)
            if m:
                vars[m.group(1)] = 0
    return vars


def get_config_h_filename():
    """Return the path of pyconfig.h."""
    if _PYTHON_BUILD:
        if os.name == "nt":
            inc_dir = os.path.join(_sys_home or _PROJECT_BASE, "PC")
        else:
            inc_dir = _sys_home or _PROJECT_BASE
    else:
        inc_dir = get_path('platinclude')
    return os.path.join(inc_dir, 'pyconfig.h')


def get_scheme_names():
    """Return a tuple containing the schemes names."""
    return tuple(sorted(_INSTALL_SCHEMES))


def get_path_names():
    """Return a tuple containing the paths names."""
    return _SCHEME_KEYS


def get_paths(scheme=get_default_scheme(), vars=None, expand=True):
    """Return a mapping containing an install scheme.

    ``scheme`` is the install scheme name. If not provided, it will
    return the default scheme for the current platform.
    """
    if expand:
        return _expand_vars(scheme, vars)
    else:
        return _INSTALL_SCHEMES[scheme]


def get_path(name, scheme=get_default_scheme(), vars=None, expand=True):
    """Return a path corresponding to the scheme.

    ``scheme`` is the install scheme name.
    """
    return get_paths(scheme, vars, expand)[name]


def get_config_vars(*args):
    """With no arguments, return a dictionary of all configuration
    variables relevant for the current platform.

    On Unix, this means every variable defined in Python's installed Makefile;
    On Windows it's a much smaller set.

    With arguments, return a list of values that result from looking up
    each argument in the configuration variable dictionary.
    """
    global _CONFIG_VARS
    if _CONFIG_VARS is None:
        _CONFIG_VARS = {}
        # Normalized versions of prefix and exec_prefix are handy to have;
        # in fact, these are the standard versions used most places in the
        # Distutils.
        _CONFIG_VARS['prefix'] = _PREFIX
        _CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX
        _CONFIG_VARS['py_version'] = _PY_VERSION
        _CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT
        _CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT
        _CONFIG_VARS['installed_base'] = _BASE_PREFIX
        _CONFIG_VARS['base'] = _PREFIX
        _CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX
        _CONFIG_VARS['platbase'] = _EXEC_PREFIX
        _CONFIG_VARS['projectbase'] = _PROJECT_BASE
        _CONFIG_VARS['platlibdir'] = sys.platlibdir
        try:
            _CONFIG_VARS['abiflags'] = sys.abiflags
        except AttributeError:
            # sys.abiflags may not be defined on all platforms.
            _CONFIG_VARS['abiflags'] = ''
        try:
            _CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '')
        except AttributeError:
            _CONFIG_VARS['py_version_nodot_plat'] = ''

        if os.name == 'nt':
            _init_non_posix(_CONFIG_VARS)
        if os.name == 'posix':
            _init_posix(_CONFIG_VARS)
        # For backward compatibility, see issue19555
        SO = _CONFIG_VARS.get('EXT_SUFFIX')
        if SO is not None:
            _CONFIG_VARS['SO'] = SO
        if _HAS_USER_BASE:
            # Setting 'userbase' is done below the call to the
            # init function to enable using 'get_config_var' in
            # the init-function.
            _CONFIG_VARS['userbase'] = _getuserbase()

        # Always convert srcdir to an absolute path
        srcdir = _CONFIG_VARS.get('srcdir', _PROJECT_BASE)
        if os.name == 'posix':
            if _PYTHON_BUILD:
                # If srcdir is a relative path (typically '.' or '..')
                # then it should be interpreted relative to the directory
                # containing Makefile.
                base = os.path.dirname(get_makefile_filename())
                srcdir = os.path.join(base, srcdir)
            else:
                # srcdir is not meaningful since the installation is
                # spread about the filesystem.  We choose the
                # directory containing the Makefile since we know it
                # exists.
                srcdir = os.path.dirname(get_makefile_filename())
        _CONFIG_VARS['srcdir'] = _safe_realpath(srcdir)

        # OS X platforms require special customization to handle
        # multi-architecture, multi-os-version installers
        if sys.platform == 'darwin':
            import _osx_support
            _osx_support.customize_config_vars(_CONFIG_VARS)

    if args:
        vals = []
        for name in args:
            vals.append(_CONFIG_VARS.get(name))
        return vals
    else:
        return _CONFIG_VARS


def get_config_var(name):
    """Return the value of a single variable using the dictionary returned by
    'get_config_vars()'.

    Equivalent to get_config_vars().get(name)
    """
    if name == 'SO':
        import warnings
        warnings.warn('SO is deprecated, use EXT_SUFFIX', DeprecationWarning, 2)
    return get_config_vars().get(name)


def get_platform():
    """Return a string that identifies the current platform.

    This is used mainly to distinguish platform-specific build directories and
    platform-specific built distributions.  Typically includes the OS name and
    version and the architecture (as supplied by 'os.uname()'), although the
    exact information included depends on the OS; on Linux, the kernel version
    isn't particularly important.

    Examples of returned values:
       linux-i586
       linux-alpha (?)
       solaris-2.6-sun4u

    Windows will return one of:
       win-amd64 (64bit Windows on AMD64 (aka x86_64, Intel64, EM64T, etc)
       win32 (all others - specifically, sys.platform is returned)

    For other non-POSIX platforms, currently just returns 'sys.platform'.

    """
    if os.name == 'nt':
        if 'amd64' in sys.version.lower():
            return 'win-amd64'
        if '(arm)' in sys.version.lower():
            return 'win-arm32'
        if '(arm64)' in sys.version.lower():
            return 'win-arm64'
        return sys.platform

    if os.name != "posix" or not hasattr(os, 'uname'):
        # XXX what about the architecture? NT is Intel or Alpha
        return sys.platform

    # Set for cross builds explicitly
    if "_PYTHON_HOST_PLATFORM" in os.environ:
        return os.environ["_PYTHON_HOST_PLATFORM"]

    # Try to distinguish various flavours of Unix
    osname, host, release, version, machine = os.uname()

    # Convert the OS name to lowercase, remove '/' characters, and translate
    # spaces (for "Power Macintosh")
    osname = osname.lower().replace('/', '')
    machine = machine.replace(' ', '_')
    machine = machine.replace('/', '-')

    if osname[:5] == "linux":
        # At least on Linux/Intel, 'machine' is the processor --
        # i386, etc.
        # XXX what about Alpha, SPARC, etc?
        return  f"{osname}-{machine}"
    elif osname[:5] == "sunos":
        if release[0] >= "5":           # SunOS 5 == Solaris 2
            osname = "solaris"
            release = f"{int(release[0]) - 3}.{release[2:]}"
            # We can't use "platform.architecture()[0]" because a
            # bootstrap problem. We use a dict to get an error
            # if some suspicious happens.
            bitness = {2147483647:"32bit", 9223372036854775807:"64bit"}
            machine += f".{bitness[sys.maxsize]}"
        # fall through to standard osname-release-machine representation
    elif osname[:3] == "aix":
        from _aix_support import aix_platform
        return aix_platform()
    elif osname[:6] == "cygwin":
        osname = "cygwin"
        import re
        rel_re = re.compile(r'[\d.]+')
        m = rel_re.match(release)
        if m:
            release = m.group()
    elif osname[:6] == "darwin":
        import _osx_support
        osname, release, machine = _osx_support.get_platform_osx(
                                            get_config_vars(),
                                            osname, release, machine)

    return f"{osname}-{release}-{machine}"


def get_python_version():
    return _PY_VERSION_SHORT


def expand_makefile_vars(s, vars):
    """Expand Makefile-style variables -- "${foo}" or "$(foo)" -- in
    'string' according to 'vars' (a dictionary mapping variable names to
    values).  Variables not present in 'vars' are silently expanded to the
    empty string.  The variable values in 'vars' should not contain further
    variable expansions; if 'vars' is the output of 'parse_makefile()',
    you're fine.  Returns a variable-expanded version of 's'.
    """
    import re

    # This algorithm does multiple expansion, so if vars['foo'] contains
    # "${bar}", it will expand ${foo} to ${bar}, and then expand
    # ${bar}... and so forth.  This is fine as long as 'vars' comes from
    # 'parse_makefile()', which takes care of such expansions eagerly,
    # according to make's variable expansion semantics.

    while True:
        m = re.search(_findvar1_rx, s) or re.search(_findvar2_rx, s)
        if m:
            (beg, end) = m.span()
            s = s[0:beg] + vars.get(m.group(1)) + s[end:]
        else:
            break
    return s


def _print_dict(title, data):
    for index, (key, value) in enumerate(sorted(data.items())):
        if index == 0:
            print(f'{title}: ')
        print(f'\t{key} = "{value}"')


def _main():
    """Display all information sysconfig detains."""
    if '--generate-posix-vars' in sys.argv:
        _generate_posix_vars()
        return
    print(f'Platform: "{get_platform()}"')
    print(f'Python version: "{get_python_version()}"')
    print(f'Current installation scheme: "{get_default_scheme()}"')
    print()
    _print_dict('Paths', get_paths())
    print()
    _print_dict('Variables', get_config_vars())


if __name__ == '__main__':
    _main()