path: root/mesonbuild/modules/python.py

# Copyright 2018 The Meson development team

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from pathlib import Path
import functools
import json
import os
import shutil
import typing as T

from . import ExtensionModule
from .. import mesonlib
from .. import mlog
from ..coredata import UserFeatureOption
from ..build import known_shmod_kwargs, EnvironmentVariables
from ..dependencies import DependencyMethods, PkgConfigDependency, NotFoundDependency, SystemDependency, ExtraFrameworkDependency
from ..dependencies.base import process_method_kw
from ..environment import detect_cpu_family
from ..interpreter import ExternalProgramHolder, extract_required_kwarg, permitted_dependency_kwargs
from ..interpreter.type_checking import NoneType
from ..interpreterbase import (
    noPosargs, noKwargs, permittedKwargs, ContainerTypeInfo,
    InvalidArguments, typed_pos_args, typed_kwargs, KwargInfo,
    FeatureNew, FeatureNewKwargs, disablerIfNotFound
)
from ..mesonlib import MachineChoice
from ..programs import ExternalProgram, NonExistingExternalProgram

if T.TYPE_CHECKING:
    from . import ModuleState
    from ..build import SharedModule, Data
    from ..dependencies import ExternalDependency, Dependency
    from ..dependencies.factory import DependencyGenerator
    from ..environment import Environment
    from ..interpreter import Interpreter
    from ..interpreterbase.interpreterbase import TYPE_var, TYPE_kwargs
    from ..backends import InstallData

    from typing_extensions import TypedDict


mod_kwargs = {'subdir'}
mod_kwargs.update(known_shmod_kwargs)
mod_kwargs -= {'name_prefix', 'name_suffix'}


if T.TYPE_CHECKING:
    _Base = ExternalDependency
else:
    _Base = object

class _PythonDependencyBase(_Base):

    def __init__(self, python_holder: 'PythonInstallation', embed: bool):
        self.name = 'python'  # override the name from the "real" dependency lookup
        self.embed = embed
        self.version: str = python_holder.version
        self.platform = python_holder.platform
        self.variables = python_holder.variables
        self.paths = python_holder.paths
        self.link_libpython = python_holder.link_libpython
        self.info: T.Optional[T.Dict[str, str]] = None
        if mesonlib.version_compare(self.version, '>= 3.0'):
            self.major_version = 3
        else:
            self.major_version = 2


class PythonPkgConfigDependency(PkgConfigDependency, _PythonDependencyBase):

    def __init__(self, name: str, environment: 'Environment',
                 kwargs: T.Dict[str, T.Any], installation: 'PythonInstallation',
                 libpc: bool = False):
        if libpc:
            mlog.debug(f'Searching for {name!r} via pkgconfig lookup in LIBPC')
        else:
            mlog.debug(f'Searching for {name!r} via fallback pkgconfig lookup in default paths')

        PkgConfigDependency.__init__(self, name, environment, kwargs)
        _PythonDependencyBase.__init__(self, installation, kwargs.get('embed', False))

        if libpc and not self.is_found:
            mlog.debug(f'"python-{self.version}" could not be found in LIBPC, this is likely due to a relocated python installation')


class PythonFrameworkDependency(ExtraFrameworkDependency, _PythonDependencyBase):

    def __init__(self, name: str, environment: 'Environment',
                 kwargs: T.Dict[str, T.Any], installation: 'PythonInstallation'):
        ExtraFrameworkDependency.__init__(self, name, environment, kwargs)
        _PythonDependencyBase.__init__(self, installation, kwargs.get('embed', False))


class PythonSystemDependency(SystemDependency, _PythonDependencyBase):

    def __init__(self, name: str, environment: 'Environment',
                 kwargs: T.Dict[str, T.Any], installation: 'PythonInstallation'):
        SystemDependency.__init__(self, name, environment, kwargs)
        _PythonDependencyBase.__init__(self, installation, kwargs.get('embed', False))

        if mesonlib.is_windows():
            self._find_libpy_windows(environment)
        else:
            self._find_libpy(installation, environment)

    def _find_libpy(self, python_holder: 'PythonInstallation', environment: 'Environment') -> None:
        if python_holder.is_pypy:
            if self.major_version == 3:
                libname = 'pypy3-c'
            else:
                libname = 'pypy-c'
            libdir = os.path.join(self.variables.get('base'), 'bin')
            libdirs = [libdir]
        else:
            libname = f'python{self.version}'
            if 'DEBUG_EXT' in self.variables:
                libname += self.variables['DEBUG_EXT']
            if 'ABIFLAGS' in self.variables:
                libname += self.variables['ABIFLAGS']
            libdirs = []

        largs = self.clib_compiler.find_library(libname, environment, libdirs)
        if largs is not None:
            self.link_args = largs

        self.is_found = largs is not None or self.link_libpython

        inc_paths = mesonlib.OrderedSet([
            self.variables.get('INCLUDEPY'),
            self.paths.get('include'),
            self.paths.get('platinclude')])

        self.compile_args += ['-I' + path for path in inc_paths if path]

    def _get_windows_python_arch(self) -> T.Optional[str]:
        if self.platform == 'mingw':
            pycc = self.variables.get('CC')
            if pycc.startswith('x86_64'):
                return '64'
            elif pycc.startswith(('i686', 'i386')):
                return '32'
            else:
                mlog.log(f'MinGW Python built with unknown CC {pycc!r}, please file a bug')
                return None
        elif self.platform == 'win32':
            return '32'
        elif self.platform in ('win64', 'win-amd64'):
            return '64'
        mlog.log(f'Unknown Windows Python platform {self.platform!r}')
        return None

    def _get_windows_link_args(self) -> T.Optional[T.List[str]]:
        if self.platform.startswith('win'):
            vernum = self.variables.get('py_version_nodot')
            if self.static:
                libpath = Path('libs') / f'libpython{vernum}.a'
            else:
                comp = self.get_compiler()
                if comp.id == "gcc":
                    libpath = Path(f'python{vernum}.dll')
                else:
                    libpath = Path('libs') / f'python{vernum}.lib'
            # base_prefix to allow for virtualenvs.
            lib = Path(self.variables.get('base_prefix')) / libpath
        elif self.platform == 'mingw':
            if self.static:
                libname = self.variables.get('LIBRARY')
            else:
                libname = self.variables.get('LDLIBRARY')
            lib = Path(self.variables.get('LIBDIR')) / libname
        else:
            raise mesonlib.MesonBugException(
                'On a Windows path, but the OS doesn\'t appear to be Windows or MinGW.')
        if not lib.exists():
            mlog.log('Could not find Python3 library {!r}'.format(str(lib)))
            return None
        return [str(lib)]

    def _find_libpy_windows(self, env: 'Environment') -> None:
        '''
        Find python3 libraries on Windows and also verify that the arch matches
        what we are building for.
        '''
        pyarch = self._get_windows_python_arch()
        if pyarch is None:
            self.is_found = False
            return
        arch = detect_cpu_family(env.coredata.compilers.host)
        if arch == 'x86':
            arch = '32'
        elif arch == 'x86_64':
            arch = '64'
        else:
            # We can't cross-compile Python 3 dependencies on Windows yet
            mlog.log(f'Unknown architecture {arch!r} for',
                     mlog.bold(self.name))
            self.is_found = False
            return
        # Pyarch ends in '32' or '64'
        if arch != pyarch:
            mlog.log('Need', mlog.bold(self.name), f'for {arch}-bit, but found {pyarch}-bit')
            self.is_found = False
            return
        # This can fail if the library is not found
        largs = self._get_windows_link_args()
        if largs is None:
            self.is_found = False
            return
        self.link_args = largs
        # Compile args
        inc_paths = mesonlib.OrderedSet([
            self.variables.get('INCLUDEPY'),
            self.paths.get('include'),
            self.paths.get('platinclude')])

        self.compile_args += ['-I' + path for path in inc_paths if path]

        # https://sourceforge.net/p/mingw-w64/mailman/message/30504611/
        if pyarch == '64' and self.major_version == 2:
            self.compile_args += ['-DMS_WIN64']

        self.is_found = True


def python_factory(env: 'Environment', for_machine: 'MachineChoice',
                   kwargs: T.Dict[str, T.Any], methods: T.List[DependencyMethods],
                   installation: 'PythonInstallation') -> T.List['DependencyGenerator']:
    # We can't use the factory_methods decorator here, as we need to pass the
    # extra installation argument
    embed = kwargs.get('embed', False)
    candidates: T.List['DependencyGenerator'] = []
    pkg_version = installation.variables.get('LDVERSION') or installation.version

    if DependencyMethods.PKGCONFIG in methods:
        pkg_libdir = installation.variables.get('LIBPC')
        pkg_embed = '-embed' if embed and mesonlib.version_compare(installation.version, '>=3.8') else ''
        pkg_name = f'python-{pkg_version}{pkg_embed}'

        # If python-X.Y.pc exists in LIBPC, we will try to use it
        def wrap_in_pythons_pc_dir(name: str, env: 'Environment', kwargs: T.Dict[str, T.Any],
                                   installation: 'PythonInstallation') -> 'ExternalDependency':
            if not pkg_libdir:
                # there is no LIBPC, so we can't search in it
                return NotFoundDependency('python', env)

            old_pkg_libdir = os.environ.pop('PKG_CONFIG_LIBDIR', None)
            old_pkg_path = os.environ.pop('PKG_CONFIG_PATH', None)
            os.environ['PKG_CONFIG_LIBDIR'] = pkg_libdir
            try:
                return PythonPkgConfigDependency(name, env, kwargs, installation, True)
            finally:
                def set_env(name, value):
                    if value is not None:
                        os.environ[name] = value
                    elif name in os.environ:
                        del os.environ[name]
                set_env('PKG_CONFIG_LIBDIR', old_pkg_libdir)
                set_env('PKG_CONFIG_PATH', old_pkg_path)

        candidates.append(functools.partial(wrap_in_pythons_pc_dir, pkg_name, env, kwargs, installation))
        # We only need to check both, if a python install has a LIBPC. It might point to the wrong location,
        # e.g. relocated / cross compilation, but the presence of LIBPC indicates we should definitely look for something.
        if pkg_libdir is not None:
            candidates.append(functools.partial(PythonPkgConfigDependency, pkg_name, env, kwargs, installation))

    if DependencyMethods.SYSTEM in methods:
        candidates.append(functools.partial(PythonSystemDependency, 'python', env, kwargs, installation))

    if DependencyMethods.EXTRAFRAMEWORK in methods:
        nkwargs = kwargs.copy()
        if mesonlib.version_compare(pkg_version, '>= 3'):
            # There is a python in /System/Library/Frameworks, but that's python 2.x,
            # Python 3 will always be in /Library
            nkwargs['paths'] = ['/Library/Frameworks']
        candidates.append(functools.partial(PythonFrameworkDependency, 'Python', env, nkwargs, installation))

    return candidates


INTROSPECT_COMMAND = '''\
import os.path
import sysconfig
import json
import sys
import distutils.command.install

def get_distutils_paths(scheme=None, prefix=None):
    import distutils.dist
    distribution = distutils.dist.Distribution()
    install_cmd = distribution.get_command_obj('install')
    if prefix is not None:
        install_cmd.prefix = prefix
    if scheme:
        install_cmd.select_scheme(scheme)
    install_cmd.finalize_options()
    return {
        'data': install_cmd.install_data,
        'include': os.path.dirname(install_cmd.install_headers),
        'platlib': install_cmd.install_platlib,
        'purelib': install_cmd.install_purelib,
        'scripts': install_cmd.install_scripts,
    }

# On Debian derivatives, the Python interpreter shipped by the distribution uses
# a custom install scheme, deb_system, for the system install, and changes the
# default scheme to a custom one pointing to /usr/local and replacing
# site-packages with dist-packages.
# See https://github.com/mesonbuild/meson/issues/8739.
# XXX: We should be using sysconfig, but Debian only patches distutils.

if 'deb_system' in distutils.command.install.INSTALL_SCHEMES:
    paths = get_distutils_paths(scheme='deb_system')
    install_paths = get_distutils_paths(scheme='deb_system', prefix='')
else:
    paths = sysconfig.get_paths()
    empty_vars = {'base': '', 'platbase': '', 'installed_base': ''}
    install_paths = sysconfig.get_paths(vars=empty_vars)

def links_against_libpython():
    from distutils.core import Distribution, Extension
    cmd = Distribution().get_command_obj('build_ext')
    cmd.ensure_finalized()
    return bool(cmd.get_libraries(Extension('dummy', [])))

variables = sysconfig.get_config_vars()
variables.update({'base_prefix': getattr(sys, 'base_prefix', sys.prefix)})

print(json.dumps({
  'variables': variables,
  'paths': paths,
  'sysconfig_paths': sysconfig.get_paths(),
  'install_paths': install_paths,
  'sys_paths': sys.path,
  'version': sysconfig.get_python_version(),
  'platform': sysconfig.get_platform(),
  'is_pypy': '__pypy__' in sys.builtin_module_names,
  'is_venv': sys.prefix != variables['base_prefix'],
  'link_libpython': links_against_libpython(),
}))
'''

if T.TYPE_CHECKING:
    class PythonIntrospectionDict(TypedDict):

        install_paths: T.Dict[str, str]
        is_pypy: bool
        is_venv: bool
        link_libpython: bool
        sysconfig_paths: T.Dict[str, str]
        paths: T.Dict[str, str]
        platform: str
        suffix: str
        variables: T.Dict[str, str]
        version: str


class PythonExternalProgram(ExternalProgram):
    def __init__(self, name: str, command: T.Optional[T.List[str]] = None,
                 ext_prog: T.Optional[ExternalProgram] = None):
        if ext_prog is None:
            super().__init__(name, command=command, silent=True)
        else:
            self.name = name
            self.command = ext_prog.command
            self.path = ext_prog.path

        # We want strong key values, so we always populate this with bogus data.
        # Otherwise to make the type checkers happy we'd have to do .get() for
        # everycall, even though we know that the introspection data will be
        # complete
        self.info: 'PythonIntrospectionDict' = {
            'install_paths': {},
            'is_pypy': False,
            'is_venv': False,
            'link_libpython': False,
            'sysconfig_paths': {},
            'paths': {},
            'platform': 'sentinal',
            'variables': {},
            'version': '0.0',
        }
        self.devenv_pythonpath: T.Set[str] = set()

    def add_devenv_pythonpath(self, basedir: str, subdir: str, install_subdir: str) -> None:
        # If we install python module into 'foo/bar' subdir, we need the last 2
        # parts of source dir to be ['foo', 'bar'] and set PYTHONPATH
        # pointing grandparent directory. That way scripts will be able to
        # `import foo.bar.something` just like when the are installed.
        # If the source tree layout does not match installed layout there is
        # nothing we can do.
        install_subdir_parts = Path(install_subdir).parts
        subdir_parts = Path(subdir).parts
        if subdir_parts[-len(install_subdir_parts):] == install_subdir_parts:
            pypath = os.path.join(basedir, *subdir_parts[:-len(install_subdir_parts)])
            self.devenv_pythonpath.add(pypath)
            print('done', pypath)

    def _check_version(self, version: str) -> bool:
        if self.name == 'python2':
            return mesonlib.version_compare(version, '< 3.0')
        elif self.name == 'python3':
            return mesonlib.version_compare(version, '>= 3.0')
        return True

    def sanity(self, state: T.Optional['ModuleState'] = None) -> bool:
        # Sanity check, we expect to have something that at least quacks in tune
        cmd = self.get_command() + ['-c', INTROSPECT_COMMAND]
        p, stdout, stderr = mesonlib.Popen_safe(cmd)
        try:
            info = json.loads(stdout)
        except json.JSONDecodeError:
            info = None
            mlog.debug('Could not introspect Python (%s): exit code %d' % (str(p.args), p.returncode))
            mlog.debug('Program stdout:\n')
            mlog.debug(stdout)
            mlog.debug('Program stderr:\n')
            mlog.debug(stderr)

        if info is not None and self._check_version(info['version']):
            variables = info['variables']
            info['suffix'] = variables.get('EXT_SUFFIX') or variables.get('SO') or variables.get('.so')
            self.info = T.cast('PythonIntrospectionDict', info)
            self.platlib = self._get_path(state, 'platlib')
            self.purelib = self._get_path(state, 'purelib')
            return True
        else:
            return False

    def _get_path(self, state: T.Optional['ModuleState'], key: str) -> None:
        rel_path = self.info['install_paths'][key][1:]
        if not state:
            # This happens only from run_project_tests.py
            return rel_path
        value = state.get_option(f'{key}dir', module='python')
        if value:
            if state.is_user_defined_option('install_env', module='python'):
                raise mesonlib.MesonException(f'python.{key}dir and python.install_env are mutually exclusive')
            return value

        install_env = state.get_option('install_env', module='python')
        if install_env == 'auto':
            install_env = 'venv' if self.info['is_venv'] else 'system'

        if install_env == 'system':
            rel_path = os.path.join(self.info['variables']['prefix'], rel_path)
        elif install_env == 'venv':
            if not self.info['is_venv']:
                raise mesonlib.MesonException('python.install_env cannot be set to "venv" unless you are in a venv!')
            # inside a venv, deb_system is *never* active hence info['paths'] may be wrong
            rel_path = self.info['sysconfig_paths'][key]

        # Use python's path relative to prefix, and warn if that's not a location
        # python will lookup for modules.
        abs_path = Path(state.get_option('prefix'), rel_path)
        sys_paths = [Path(i) for i in self.info['sys_paths']]
        if abs_path not in sys_paths:
            mlog.warning('Python files installed by Meson might not be found by python interpreter.\n',
                         f'This warning can be avoided by setting "python.{key}dir" option.',
                         once=True)
        return rel_path


_PURE_KW = KwargInfo('pure', bool, default=True)
_SUBDIR_KW = KwargInfo('subdir', str, default='')

if T.TYPE_CHECKING:

    class PyInstallKw(TypedDict):

        pure: bool
        subdir: str
        install_tag: T.Optional[str]


class PythonInstallation(ExternalProgramHolder):
    def __init__(self, python: 'PythonExternalProgram', interpreter: 'Interpreter'):
        ExternalProgramHolder.__init__(self, python, interpreter)
        info = python.info
        prefix = self.interpreter.environment.coredata.get_option(mesonlib.OptionKey('prefix'))
        assert isinstance(prefix, str), 'for mypy'
        self.variables = info['variables']
        self.suffix = info['suffix']
        self.paths = info['paths']
        self.platlib_install_path = os.path.join(prefix, python.platlib)
        self.purelib_install_path = os.path.join(prefix, python.purelib)
        self.version = info['version']
        self.platform = info['platform']
        self.is_pypy = info['is_pypy']
        self.link_libpython = info['link_libpython']
        self.methods.update({
            'extension_module': self.extension_module_method,
            'dependency': self.dependency_method,
            'install_sources': self.install_sources_method,
            'get_install_dir': self.get_install_dir_method,
            'language_version': self.language_version_method,
            'found': self.found_method,
            'has_path': self.has_path_method,
            'get_path': self.get_path_method,
            'has_variable': self.has_variable_method,
            'get_variable': self.get_variable_method,
            'path': self.path_method,
        })

    @permittedKwargs(mod_kwargs)
    def extension_module_method(self, args: T.List['TYPE_var'], kwargs: 'TYPE_kwargs') -> 'SharedModule':
        if 'install_dir' in kwargs:
            if 'subdir' in kwargs:
                raise InvalidArguments('"subdir" and "install_dir" are mutually exclusive')
        else:
            subdir = kwargs.pop('subdir', '')
            if not isinstance(subdir, str):
                raise InvalidArguments('"subdir" argument must be a string.')
            kwargs['install_dir'] = os.path.join(self.platlib_install_path, subdir)
            self.held_object.add_devenv_pythonpath(
                self.interpreter.environment.get_build_dir(),
                self.interpreter.subdir, subdir)

        # On macOS and some Linux distros (Debian) distutils doesn't link
        # extensions against libpython. We call into distutils and mirror its
        # behavior. See https://github.com/mesonbuild/meson/issues/4117
        if not self.link_libpython:
            new_deps = []
            for dep in mesonlib.extract_as_list(kwargs, 'dependencies'):
                if isinstance(dep, _PythonDependencyBase):
                    dep = dep.get_partial_dependency(compile_args=True)
                new_deps.append(dep)
            kwargs['dependencies'] = new_deps

        # msys2's python3 has "-cpython-36m.dll", we have to be clever
        # FIXME: explain what the specific cleverness is here
        split, suffix = self.suffix.rsplit('.', 1)
        args[0] += split

        kwargs['name_prefix'] = ''
        kwargs['name_suffix'] = suffix

        return self.interpreter.func_shared_module(None, args, kwargs)

    @disablerIfNotFound
    @permittedKwargs(permitted_dependency_kwargs | {'embed'})
    @FeatureNewKwargs('python_installation.dependency', '0.53.0', ['embed'])
    @noPosargs
    def dependency_method(self, args: T.List['TYPE_var'], kwargs: 'TYPE_kwargs') -> 'Dependency':
        disabled, required, feature = extract_required_kwarg(kwargs, self.subproject)
        # it's theoretically (though not practically) possible for the else clse
        # to not bind dep, let's ensure it is.
        dep: 'Dependency' = NotFoundDependency('python', self.interpreter.environment)
        if disabled:
            mlog.log('Dependency', mlog.bold('python'), 'skipped: feature', mlog.bold(feature), 'disabled')
        else:
            new_kwargs = kwargs.copy()
            new_kwargs['required'] = False
            methods = process_method_kw({DependencyMethods.PKGCONFIG, DependencyMethods.SYSTEM}, kwargs)
            for d in python_factory(self.interpreter.environment,
                                    MachineChoice.BUILD if kwargs.get('native', False) else MachineChoice.HOST,
                                    new_kwargs, methods, self):
                dep = d()
                if dep.found():
                    break
            if required and not dep.found():
                raise mesonlib.MesonException('Python dependency not found')

        return dep

    @typed_pos_args('install_data', varargs=(str, mesonlib.File))
    @typed_kwargs('python_installation.install_sources', _PURE_KW, _SUBDIR_KW,
                  KwargInfo('install_tag', (str, NoneType), since='0.60.0'))
    def install_sources_method(self, args: T.Tuple[T.List[T.Union[str, mesonlib.File]]],
                               kwargs: 'PyInstallKw') -> 'Data':
        tag = kwargs['install_tag'] or 'runtime'
        pure = kwargs['pure']
        sources = self.interpreter.source_strings_to_files(args[0])
        install_subdir = kwargs['subdir']
        install_dir = self._get_install_dir_impl(pure, install_subdir)
        builddir = self.interpreter.environment.get_build_dir()
        srcdir = self.interpreter.environment.get_source_dir()
        for src in sources:
            basedir = builddir if src.is_built else srcdir
            subdir = os.path.dirname(src.relative_name())
            self.held_object.add_devenv_pythonpath(basedir, subdir, install_subdir)
        return self.interpreter.install_data_impl(sources, install_dir,
            mesonlib.FileMode(), rename=None, tag=tag, install_data_type='python',
            install_dir_name=self._get_install_dir_name_impl(pure, install_subdir))

    @noPosargs
    @typed_kwargs('python_installation.install_dir', _PURE_KW, _SUBDIR_KW)
    def get_install_dir_method(self, args: T.List['TYPE_var'], kwargs: 'PyInstallKw') -> str:
        return self._get_install_dir_impl(kwargs['pure'], kwargs['subdir'])

    def _get_install_dir_impl(self, pure: bool, subdir: str) -> str:
        return os.path.join(
            self.purelib_install_path if pure else self.platlib_install_path, subdir)

    def _get_install_dir_name_impl(self, pure: bool, subdir: str) -> str:
        return os.path.join('{py_purelib}' if pure else '{py_platlib}', subdir)

    @noPosargs
    @noKwargs
    def language_version_method(self, args: T.List['TYPE_var'], kwargs: 'TYPE_kwargs') -> str:
        return self.version

    @typed_pos_args('python_installation.has_path', str)
    @noKwargs
    def has_path_method(self, args: T.Tuple[str], kwargs: 'TYPE_kwargs') -> bool:
        return args[0] in self.paths

    @typed_pos_args('python_installation.get_path', str, optargs=[object])
    @noKwargs
    def get_path_method(self, args: T.Tuple[str, T.Optional['TYPE_var']], kwargs: 'TYPE_kwargs') -> 'TYPE_var':
        path_name, fallback = args
        try:
            return self.paths[path_name]
        except KeyError:
            if fallback is not None:
                return fallback
            raise InvalidArguments(f'{path_name} is not a valid path name')

    @typed_pos_args('python_installation.has_variable', str)
    @noKwargs
    def has_variable_method(self, args: T.Tuple[str], kwargs: 'TYPE_kwargs') -> bool:
        return args[0] in self.variables

    @typed_pos_args('python_installation.get_variable', str, optargs=[object])
    @noKwargs
    def get_variable_method(self, args: T.Tuple[str, T.Optional['TYPE_var']], kwargs: 'TYPE_kwargs') -> 'TYPE_var':
        var_name, fallback = args
        try:
            return self.variables[var_name]
        except KeyError:
            if fallback is not None:
                return fallback
            raise InvalidArguments(f'{var_name} is not a valid variable name')

    @noPosargs
    @noKwargs
    @FeatureNew('Python module path method', '0.50.0')
    def path_method(self, args: T.List['TYPE_var'], kwargs: 'TYPE_kwargs') -> str:
        return super().path_method(args, kwargs)


if T.TYPE_CHECKING:
    from ..interpreter.kwargs import ExtractRequired

    class FindInstallationKw(ExtractRequired):

        disabler: bool
        modules: T.List[str]


class PythonModule(ExtensionModule):

    @FeatureNew('Python Module', '0.46.0')
    def __init__(self, interpreter: 'Interpreter') -> None:
        super().__init__(interpreter)
        self.installations: T.Dict[str, ExternalProgram] = {}
        self.methods.update({
            'find_installation': self.find_installation,
        })

    def get_devenv(self) -> T.Optional[EnvironmentVariables]:
        pythonpath = set()
        for python in self.installations.values():
            version = python.info['version']
            if mesonlib.version_compare(version, '>=3.0'):
                pythonpath |= python.devenv_pythonpath
        if pythonpath:
            env = EnvironmentVariables()
            env.prepend('PYTHONPATH', list(pythonpath))
            return env
        return None

    # https://www.python.org/dev/peps/pep-0397/
    @staticmethod
    def _get_win_pythonpath(name_or_path: str) -> T.Optional[str]:
        if name_or_path not in ['python2', 'python3']:
            return None
        if not shutil.which('py'):
            # program not installed, return without an exception
            return None
        ver = {'python2': '-2', 'python3': '-3'}[name_or_path]
        cmd = ['py', ver, '-c', "import sysconfig; print(sysconfig.get_config_var('BINDIR'))"]
        _, stdout, _ = mesonlib.Popen_safe(cmd)
        directory = stdout.strip()
        if os.path.exists(directory):
            return os.path.join(directory, 'python')
        else:
            return None

    def _find_installation_impl(self, state: 'ModuleState', display_name: str, name_or_path: str) -> ExternalProgram:
        if not name_or_path:
            python = PythonExternalProgram('python3', mesonlib.python_command)
        else:
            tmp_python = ExternalProgram.from_entry(display_name, name_or_path)
            python = PythonExternalProgram(display_name, ext_prog=tmp_python)

            if not python.found() and mesonlib.is_windows():
                pythonpath = self._get_win_pythonpath(name_or_path)
                if pythonpath is not None:
                    name_or_path = pythonpath
                    python = PythonExternalProgram(name_or_path)

            # Last ditch effort, python2 or python3 can be named python
            # on various platforms, let's not give up just yet, if an executable
            # named python is available and has a compatible version, let's use
            # it
            if not python.found() and name_or_path in ['python2', 'python3']:
                python = PythonExternalProgram('python')

        if python.found() and not python.sanity(state):
            python = NonExistingExternalProgram()

        return python

    @disablerIfNotFound
    @typed_pos_args('python.find_installation', optargs=[str])
    @typed_kwargs(
        'python.find_installation',
        KwargInfo('required', (bool, UserFeatureOption), default=True),
        KwargInfo('disabler', bool, default=False, since='0.49.0'),
        KwargInfo('modules', ContainerTypeInfo(list, str), listify=True, default=[], since='0.51.0'),
    )
    def find_installation(self, state: 'ModuleState', args: T.Tuple[T.Optional[str]],
                          kwargs: 'FindInstallationKw') -> ExternalProgram:
        feature_check = FeatureNew('Passing "feature" option to find_installation', '0.48.0')
        disabled, required, feature = extract_required_kwarg(kwargs, state.subproject, feature_check)

        # FIXME: this code is *full* of sharp corners. It assumes that it's
        # going to get a string value (or now a list of length 1), of `python2`
        # or `python3` which is completely nonsense.  On windows the value could
        # easily be `['py', '-3']`, or `['py', '-3.7']` to get a very specific
        # version of python. On Linux we might want a python that's not in
        # $PATH, or that uses a wrapper of some kind.
        np: T.List[str] = state.environment.lookup_binary_entry(MachineChoice.HOST, 'python') or []
        fallback = args[0]
        display_name = fallback or 'python'
        if not np and fallback is not None:
            np = [fallback]
        name_or_path = np[0] if np else None

        if disabled:
            mlog.log('Program', name_or_path or 'python', 'found:', mlog.red('NO'), '(disabled by:', mlog.bold(feature), ')')
            return NonExistingExternalProgram()

        python = self.installations.get(name_or_path)
        if not python:
            python = self._find_installation_impl(state, display_name, name_or_path)
            self.installations[name_or_path] = python

        want_modules = kwargs['modules']
        found_modules: T.List[str] = []
        missing_modules: T.List[str] = []
        if python.found() and want_modules:
            for mod in want_modules:
                p, *_ = mesonlib.Popen_safe(
                    python.command +
                    ['-c', f'import {mod}'])
                if p.returncode != 0:
                    missing_modules.append(mod)
                else:
                    found_modules.append(mod)

        msg: T.List['mlog.TV_Loggable'] = ['Program', python.name]
        if want_modules:
            msg.append('({})'.format(', '.join(want_modules)))
        msg.append('found:')
        if python.found() and not missing_modules:
            msg.extend([mlog.green('YES'), '({})'.format(' '.join(python.command))])
        else:
            msg.append(mlog.red('NO'))
        if found_modules:
            msg.append('modules:')
            msg.append(', '.join(found_modules))

        mlog.log(*msg)

        if not python.found():
            if required:
                raise mesonlib.MesonException('{} not found'.format(name_or_path or 'python'))
            return NonExistingExternalProgram()
        elif missing_modules:
            if required:
                raise mesonlib.MesonException('{} is missing modules: {}'.format(name_or_path or 'python', ', '.join(missing_modules)))
            return NonExistingExternalProgram()
        else:
            return python

        raise mesonlib.MesonBugException('Unreachable code was reached (PythonModule.find_installation).')


def initialize(interpreter: 'Interpreter') -> PythonModule:
    mod = PythonModule(interpreter)
    mod.interpreter.append_holder_map(PythonExternalProgram, PythonInstallation)
    return mod