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Diffstat (limited to 'Doc/library/importlib.rst')
| -rw-r--r-- | Doc/library/importlib.rst | 35 |
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diff --git a/Doc/library/importlib.rst b/Doc/library/importlib.rst index afdae9e..a83e5e4 100644 --- a/Doc/library/importlib.rst +++ b/Doc/library/importlib.rst @@ -1191,3 +1191,38 @@ an :term:`importer`. module will be file-based. .. versionadded:: 3.4 + +.. class:: LazyLoader(loader) + + A class which postpones the execution of the loader of a module until the + module has an attribute accessed. + + This class **only** works with loaders that define + :meth:`importlib.abc.Loader.exec_module` as control over what module type + is used for the module is required. For the same reasons, the loader + **cannot** define :meth:`importlib.abc.Loader.create_module`. Finally, + modules which substitute the object placed into :attr:`sys.modules` will + not work as there is no way to properly replace the module references + throughout the interpreter safely; :exc:`ValueError` is raised if such a + substitution is detected. + + .. note:: + For projects where startup time is critical, this class allows for + potentially minimizing the cost of loading a module if it is never used. + For projects where startup time is not essential then use of this class is + **heavily** discouraged due to error messages created during loading being + postponed and thus occurring out of context. + + .. versionadded:: 3.5 + + .. classmethod:: factory(loader) + + A static method which returns a callable that creates a lazy loader. This + is meant to be used in situations where the loader is passed by class + instead of by instance. + :: + + suffixes = importlib.machinery.SOURCE_SUFFIXES + loader = importlib.machinery.SourceFileLoader + lazy_loader = importlib.util.LazyLoader.factory(loader) + finder = importlib.machinery.FileFinder(path, [(lazy_loader, suffixes)]) |