Python sys.meta_path() Examples

def find_loader(name, path=None):
    """Find the loader for the specified module.

    First, sys.modules is checked to see if the module was already imported. If
    so, then sys.modules[name].__loader__ is returned. If that happens to be
    set to None, then ValueError is raised. If the module is not in
    sys.modules, then sys.meta_path is searched for a suitable loader with the
    value of 'path' given to the finders. None is returned if no loader could
    be found.

    Dotted names do not have their parent packages implicitly imported. You will
    most likely need to explicitly import all parent packages in the proper
    order for a submodule to get the correct loader.

    """
    try:
        loader = sys.modules[name].__loader__
        if loader is None:
            raise ValueError('{}.__loader__ is None'.format(name))
        else:
            return loader
    except KeyError:
        pass
    return _bootstrap._find_module(name, path) 

def remove_hooks(scrub_sys_modules=False):
    """
    This function removes the import hook from sys.meta_path.
    """
    if PY3:
        return
    flog.debug('Uninstalling hooks ...')
    # Loop backwards, so deleting items keeps the ordering:
    for i, hook in list(enumerate(sys.meta_path))[::-1]:
        if hasattr(hook, 'RENAMER'):
            del sys.meta_path[i]

    # Explicit is better than implicit. In the future the interface should
    # probably change so that scrubbing the import hooks requires a separate
    # function call. Left as is for now for backward compatibility with
    # v0.11.x.
    if scrub_sys_modules:
        scrub_future_sys_modules() 

def install_hooks():
    """
    This function installs the future.standard_library import hook into
    sys.meta_path.
    """
    if PY3:
        return

    install_aliases()

    flog.debug('sys.meta_path was: {0}'.format(sys.meta_path))
    flog.debug('Installing hooks ...')

    # Add it unless it's there already
    newhook = RenameImport(RENAMES)
    if not detect_hooks():
        sys.meta_path.append(newhook)
    flog.debug('sys.meta_path is now: {0}'.format(sys.meta_path)) 

def install_hooks():
    """
    This function installs the future.standard_library import hook into
    sys.meta_path.
    """
    if PY3:
        return

    install_aliases()

    flog.debug('sys.meta_path was: {0}'.format(sys.meta_path))
    flog.debug('Installing hooks ...')

    # Add it unless it's there already
    newhook = RenameImport(RENAMES)
    if not detect_hooks():
        sys.meta_path.append(newhook)
    flog.debug('sys.meta_path is now: {0}'.format(sys.meta_path)) 

def remove_hooks(scrub_sys_modules=False):
    """
    This function removes the import hook from sys.meta_path.
    """
    if PY3:
        return
    flog.debug('Uninstalling hooks ...')
    # Loop backwards, so deleting items keeps the ordering:
    for i, hook in list(enumerate(sys.meta_path))[::-1]:
        if hasattr(hook, 'RENAMER'):
            del sys.meta_path[i]

    # Explicit is better than implicit. In the future the interface should
    # probably change so that scrubbing the import hooks requires a separate
    # function call. Left as is for now for backward compatibility with
    # v0.11.x.
    if scrub_sys_modules:
        scrub_future_sys_modules() 

def detect_hooks():
    """
    Returns True if the import hooks are installed, False if not.
    """
    flog.debug('Detecting hooks ...')
    present = any([hasattr(hook, 'RENAMER') for hook in sys.meta_path])
    if present:
        flog.debug('Detected.')
    else:
        flog.debug('Not detected.')
    return present


# As of v0.12, this no longer happens implicitly:
# if not PY3:
#     install_hooks() 

def mount(self, append=False):
        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
        if not self.is_compatible():
            msg = 'Wheel %s not compatible with this Python.' % pathname
            raise DistlibException(msg)
        if not self.is_mountable():
            msg = 'Wheel %s is marked as not mountable.' % pathname
            raise DistlibException(msg)
        if pathname in sys.path:
            logger.debug('%s already in path', pathname)
        else:
            if append:
                sys.path.append(pathname)
            else:
                sys.path.insert(0, pathname)
            extensions = self._get_extensions()
            if extensions:
                if _hook not in sys.meta_path:
                    sys.meta_path.append(_hook)
                _hook.add(pathname, extensions) 

def mount(self, append=False):
        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
        if not self.is_compatible():
            msg = 'Wheel %s not compatible with this Python.' % pathname
            raise DistlibException(msg)
        if not self.is_mountable():
            msg = 'Wheel %s is marked as not mountable.' % pathname
            raise DistlibException(msg)
        if pathname in sys.path:
            logger.debug('%s already in path', pathname)
        else:
            if append:
                sys.path.append(pathname)
            else:
                sys.path.insert(0, pathname)
            extensions = self._get_extensions()
            if extensions:
                if _hook not in sys.meta_path:
                    sys.meta_path.append(_hook)
                _hook.add(pathname, extensions) 

def install_hooks():
    """
    This function installs the future.standard_library import hook into
    sys.meta_path.
    """
    if PY3:
        return

    install_aliases()

    flog.debug('sys.meta_path was: {0}'.format(sys.meta_path))
    flog.debug('Installing hooks ...')

    # Add it unless it's there already
    newhook = RenameImport(RENAMES)
    if not detect_hooks():
        sys.meta_path.append(newhook)
    flog.debug('sys.meta_path is now: {0}'.format(sys.meta_path)) 

def remove_hooks(scrub_sys_modules=False):
    """
    This function removes the import hook from sys.meta_path.
    """
    if PY3:
        return
    flog.debug('Uninstalling hooks ...')
    # Loop backwards, so deleting items keeps the ordering:
    for i, hook in list(enumerate(sys.meta_path))[::-1]:
        if hasattr(hook, 'RENAMER'):
            del sys.meta_path[i]

    # Explicit is better than implicit. In the future the interface should
    # probably change so that scrubbing the import hooks requires a separate
    # function call. Left as is for now for backward compatibility with
    # v0.11.x.
    if scrub_sys_modules:
        scrub_future_sys_modules() 

def mount(self, append=False):
        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
        if not self.is_compatible():
            msg = 'Wheel %s not compatible with this Python.' % pathname
            raise DistlibException(msg)
        if not self.is_mountable():
            msg = 'Wheel %s is marked as not mountable.' % pathname
            raise DistlibException(msg)
        if pathname in sys.path:
            logger.debug('%s already in path', pathname)
        else:
            if append:
                sys.path.append(pathname)
            else:
                sys.path.insert(0, pathname)
            extensions = self._get_extensions()
            if extensions:
                if _hook not in sys.meta_path:
                    sys.meta_path.append(_hook)
                _hook.add(pathname, extensions) 

def _add_git_repo(url_builder, username=None, repo=None, module=None, branch=None, commit=None, **kw):
    '''
Function that creates and adds to the 'sys.meta_path' an HttpImporter object equipped with a URL of a Online Git server.
The 'url_builder' parameter is a function that accepts the username, repo and branch/commit, and creates a HTTP/S URL of a Git server. Compatible functions are '__create_github_url', '__create_bitbucket_url'.
The 'username' parameter defines the Github username which is the repository's owner.
The 'repo' parameter defines the name of the repo that contains the modules/packages to be imported.
The 'module' parameter is optional and is a list containing the modules/packages that are available in the chosen Github repository.
If it is not provided, it defaults to the repositories name, as it is common that the a Python repository at "github.com/someuser/somereponame" contains a module/package of "somereponame".
The 'branch' and 'commit' parameters cannot be both populated at the same call. They specify the branch (last commit) or specific commit, that should be served.
    '''
    if username == None or repo == None:
        raise Error("'username' and 'repo' parameters cannot be None")
    if commit and branch:
        raise Error("'branch' and 'commit' parameters cannot be both set!")

    if commit:
        branch = commit
    if not branch:
        branch = 'master'
    if not module:
        module = repo
    if type(module) == str:
        module = [module]
    url = url_builder(username, repo, branch, **kw)
    return add_remote_repo(module, url) 

def _FakeProxyBypassHelper(fn,
                             original_module_dict=sys.modules.copy(),
                             original_uname=os.uname):
    """Setups and restores the state for the Mac OS X urllib fakes."""
    def Inner(*args, **kwargs):
      current_uname = os.uname
      current_meta_path = sys.meta_path[:]
      current_modules = sys.modules.copy()

      try:
        sys.modules.clear()
        sys.modules.update(original_module_dict)
        sys.meta_path[:] = []
        os.uname = original_uname

        return fn(*args, **kwargs)
      finally:
        sys.modules.clear()
        sys.modules.update(current_modules)
        os.uname = current_uname
        sys.meta_path[:] = current_meta_path
    return Inner 

def ResetModules(self):
    """Clear modules so that when request is run they are reloaded."""
    lib_config._default_registry.reset()
    self._modules.clear()
    self._modules.update(self._default_modules)


    sys.path_hooks[:] = self._save_path_hooks


    sys.meta_path = []





    apiproxy_stub_map.apiproxy.GetPreCallHooks().Clear()
    apiproxy_stub_map.apiproxy.GetPostCallHooks().Clear() 

def mount(self, append=False):
        pathname = os.path.abspath(os.path.join(self.dirname, self.filename))
        if not self.is_compatible():
            msg = 'Wheel %s not compatible with this Python.' % pathname
            raise DistlibException(msg)
        if not self.is_mountable():
            msg = 'Wheel %s is marked as not mountable.' % pathname
            raise DistlibException(msg)
        if pathname in sys.path:
            logger.debug('%s already in path', pathname)
        else:
            if append:
                sys.path.append(pathname)
            else:
                sys.path.insert(0, pathname)
            extensions = self._get_extensions()
            if extensions:
                if _hook not in sys.meta_path:
                    sys.meta_path.append(_hook)
                _hook.add(pathname, extensions) 

def register_assert_rewrite(*names):
    """Register one or more module names to be rewritten on import.

    This function will make sure that this module or all modules inside
    the package will get their assert statements rewritten.
    Thus you should make sure to call this before the module is
    actually imported, usually in your __init__.py if you are a plugin
    using a package.

    :raise TypeError: if the given module names are not strings.
    """
    for name in names:
        if not isinstance(name, str):
            msg = "expected module names as *args, got {0} instead"
            raise TypeError(msg.format(repr(names)))
    for hook in sys.meta_path:
        if isinstance(hook, rewrite.AssertionRewritingHook):
            importhook = hook
            break
    else:
        importhook = DummyRewriteHook()
    importhook.mark_rewrite(*names) 

def testImpWrapper(self):
        i = ImpWrapper()
        sys.meta_path.append(i)
        sys.path_hooks.append(ImpWrapper)
        mnames = ("colorsys", "urlparse", "distutils.core", "compiler.misc")
        for mname in mnames:
            parent = mname.split(".")[0]
            for n in sys.modules.keys():
                if n.startswith(parent):
                    del sys.modules[n]
        with test_support.check_warnings(("The compiler package is deprecated "
                                          "and removed", DeprecationWarning)):
            for mname in mnames:
                m = __import__(mname, globals(), locals(), ["__dummy__"])
                m.__loader__  # to make sure we actually handled the import 

def remote_repo(modules, base_url='http://localhost:8000/', zip_pwd=None):
    '''
Context Manager that provides remote import functionality through a URL.
The parameters are the same as the HttpImporter class contructor.
    '''
    importer = add_remote_repo(modules, base_url, zip_pwd=zip_pwd)
    try:
        yield
    except ImportError as e:
        raise e
    finally:    # Always remove the added HttpImporter from sys.meta_path 
        remove_remote_repo(base_url)


# Default 'python -m SimpleHTTPServer' URL 

def tearDown(self):
        sys.path[:] = self.path
        sys.meta_path[:] = self.meta_path
        sys.path_hooks[:] = self.path_hooks
        sys.path_importer_cache.clear()
        sys.modules.clear()
        sys.modules.update(self.modules_before) 

def find_module(self, fullname, path=None):
        # Note: we ignore 'path' argument since it is only used via meta_path
        subname = fullname.split(".")[-1]
        if subname != fullname and self.path is None:
            return None
        if self.path is None:
            path = None
        else:
            path = [os.path.realpath(self.path)]
        try:
            file, filename, etc = imp.find_module(subname, path)
        except ImportError:
            return None
        return ImpLoader(fullname, file, filename, etc) 

def install(self):
        """
        Install this importer into sys.meta_path if not already present.
        """
        if self not in sys.meta_path:
            sys.meta_path.append(self) 

def install(self):
        """
        Install this importer into sys.meta_path if not already present.
        """
        if self not in sys.meta_path:
            sys.meta_path.append(self) 

def iter_importers(fullname=""):
    """Yield PEP 302 importers for the given module name

    If fullname contains a '.', the importers will be for the package
    containing fullname, otherwise they will be importers for sys.meta_path,
    sys.path, and Python's "classic" import machinery, in that order.  If
    the named module is in a package, that package is imported as a side
    effect of invoking this function.

    Non PEP 302 mechanisms (e.g. the Windows registry) used by the
    standard import machinery to find files in alternative locations
    are partially supported, but are searched AFTER sys.path. Normally,
    these locations are searched BEFORE sys.path, preventing sys.path
    entries from shadowing them.

    For this to cause a visible difference in behaviour, there must
    be a module or package name that is accessible via both sys.path
    and one of the non PEP 302 file system mechanisms. In this case,
    the emulation will find the former version, while the builtin
    import mechanism will find the latter.

    Items of the following types can be affected by this discrepancy:
        imp.C_EXTENSION, imp.PY_SOURCE, imp.PY_COMPILED, imp.PKG_DIRECTORY
    """
    if fullname.startswith('.'):
        raise ImportError("Relative module names not supported")
    if '.' in fullname:
        # Get the containing package's __path__
        pkg = '.'.join(fullname.split('.')[:-1])
        if pkg not in sys.modules:
            __import__(pkg)
        path = getattr(sys.modules[pkg], '__path__', None) or []
    else:
        for importer in sys.meta_path:
            yield importer
        path = sys.path
    for item in path:
        yield get_importer(item)
    if '.' not in fullname:
        yield ImpImporter() 

def setUp(self):
        sys.meta_path.insert(0, self.MyTestImporter()) 

def tearDown(self):
        del sys.meta_path[0] 

def install(self):
        """
        Install this importer into sys.meta_path if not already present.
        """
        if self not in sys.meta_path:
            sys.meta_path.append(self) 

def restore(self):
        sys.path[:], sys.meta_path[:] = self.__saved 

def install(self):
        """
        Install this importer into sys.meta_path if not already present.
        """
        if self not in sys.meta_path:
            sys.meta_path.append(self) 

def test_import_hooks_importer(self):
        """importer tests - verify the importer gets passed correct values, handles
        errors coming back out correctly"""
        global myimpCalled
        myimpCalled = None
        
        class myimp(object):
            def find_module(self, fullname, path=None):
                global myimpCalled
                myimpCalled = fullname, path
                if fullname == 'does_not_exist_throw':
                    raise Exception('hello')
        
        mi = myimp()
        sys.meta_path.append(mi)
        try:
            try:
                import does_not_exist
                self.assertUnreachable()
            except ImportError: pass
            
            self.assertEqual(myimpCalled, ('does_not_exist', None))
            
            try:
                from testpkg1 import blah
                self.assertUnreachable()
            except ImportError:
                pass

            self.assertEqual(type(myimpCalled[1]), list)
            self.assertEqual(myimpCalled[0], 'testpkg1.blah')
            self.assertEqual(myimpCalled[1][0][-8:], 'testpkg1')
            
            def f(): import does_not_exist_throw
            
            self.assertRaisesMessage(Exception, 'hello', f)
        finally:
            sys.meta_path.remove(mi)

    #TODO: @skip("multiple_execute") 

def testMetaPath(self):
        i = MetaImporter()
        sys.meta_path.append(i)
        self.doTestImports(i)