# `importlib` — The implementation of `import`

Added in version 3.1.

Source code: Lib/importlib/__init__.py

## Introduction

The purpose of the `importlib` package is three-fold.

One is to provide the implementation of the `import` statement (and thus, by extension, the `__import__()` function) in Python source code. This provides an implementation of `import` which is portable to any Python interpreter. This also provides an implementation which is easier to comprehend than one implemented in a programming language other than Python.

Two, the components to implement `import` are exposed in this package, making it easier for users to create their own custom objects (known generically as an importer) to participate in the import process.

Three, the package contains modules exposing additional functionality for managing aspects of Python packages:

- `importlib.metadata` presents access to metadata from third-party distributions.

- `importlib.resources` provides routines for accessing non-code “resources” from Python packages.

See also

The import statement

  The language reference for the `import` statement.

Packages specification

  Original specification of packages. Some semantics have changed since the writing of this document (e.g. redirecting based on `None` in `sys.modules`).

The `__import__()` function

  The `import` statement is syntactic sugar for this function.

The initialization of the sys.path module search path

  The initialization of `sys.path`.

PEP 235

  Import on Case-Insensitive Platforms

PEP 263

  Defining Python Source Code Encodings

PEP 302

  New Import Hooks

PEP 328

  Imports: Multi-Line and Absolute/Relative

PEP 366

  Main module explicit relative imports

PEP 420

  Implicit namespace packages

PEP 451

  A ModuleSpec Type for the Import System

PEP 488

  Elimination of PYO files

PEP 489

  Multi-phase extension module initialization

PEP 552

  Deterministic pycs

PEP 3120

  Using UTF-8 as the Default Source Encoding

PEP 3147

  PYC Repository Directories

## Functions

importlib.__import__(name, globals=None, locals=None, fromlist=(), level=0)

  An implementation of the built-in `__import__()` function.

  Note

  Programmatic importing of modules should use `import_module()` instead of this function.

importlib.import_module(name, package=None)

  Import a module. The name argument specifies what module to import in absolute or relative terms (e.g. either `pkg.mod` or `..mod`). If the name is specified in relative terms, then the package argument must be set to the name of the package which is to act as the anchor for resolving the package name (e.g. `import_module('..mod', 'pkg.subpkg')` will import `pkg.mod`).

  The `import_module()` function acts as a simplifying wrapper around `importlib.__import__()`. This means all semantics of the function are derived from `importlib.__import__()`. The most important difference between these two functions is that `import_module()` returns the specified package or module (e.g. `pkg.mod`), while `__import__()` returns the top-level package or module (e.g. `pkg`).

  If you are dynamically importing a module that was created since the interpreter began execution (e.g., created a Python source file), you may need to call `invalidate_caches()` in order for the new module to be noticed by the import system.

  Changed in version 3.3: Parent packages are automatically imported.

importlib.invalidate_caches()

  Invalidate the internal caches of finders stored at `sys.meta_path`. If a finder implements `invalidate_caches()` then it will be called to perform the invalidation. This function should be called if any modules are created/installed while your program is running to guarantee all finders will notice the new module’s existence.

  Added in version 3.3.

  Changed in version 3.10: Namespace packages created/installed in a different `sys.path` location after the same namespace was already imported are noticed.

importlib.reload(module)

  Reload a previously imported module. The argument must be a module object, so it must have been successfully imported before. This is useful if you have edited the module source file using an external editor and want to try out the new version without leaving the Python interpreter. The return value is the module object (which can be different if re-importing causes a different object to be placed in `sys.modules`).

  When `reload()` is executed:

  - Python module’s code is recompiled and the module-level code re-executed, defining a new set of objects which are bound to names in the module’s dictionary by reusing the loader which originally loaded the module. The `init` function of extension modules is not called a second time.

  - As with all other objects in Python the old objects are only reclaimed after their reference counts drop to zero.

  - The names in the module namespace are updated to point to any new or changed objects.

  - Other references to the old objects (such as names external to the module) are not rebound to refer to the new objects and must be updated in each namespace where they occur if that is desired.

  There are a number of other caveats:

  When a module is reloaded, its dictionary (containing the module’s global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem. If the new version of a module does not define a name that was defined by the old version, the old definition remains. This feature can be used to the module’s advantage if it maintains a global table or cache of objects — with a `try` statement it can test for the table’s presence and skip its initialization if desired:

      try:
          cache
      except NameError:
          cache = {}

  It is generally not very useful to reload built-in or dynamically loaded modules. Reloading `sys`, `__main__`, `builtins` and other key modules is not recommended. In many cases extension modules are not designed to be initialized more than once, and may fail in arbitrary ways when reloaded.

  If a module imports objects from another module using `from` … `import` …, calling `reload()` for the other module does not redefine the objects imported from it — one way around this is to re-execute the `from` statement, another is to use `import` and qualified names (module.name) instead.

  If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances — they continue to use the old class definition. The same is true for derived classes.

  Added in version 3.4.

  Changed in version 3.7: `ModuleNotFoundError` is raised when the module being reloaded lacks a `ModuleSpec`.

## `importlib.abc` – Abstract base classes related to import

Source code: Lib/importlib/abc.py

The `importlib.abc` module contains all of the core abstract base classes used by `import`. Some subclasses of the core abstract base classes are also provided to help in implementing the core ABCs.

ABC hierarchy:

    object
     +-- MetaPathFinder
     +-- PathEntryFinder
     +-- Loader
          +-- ResourceLoader --------+
          +-- InspectLoader          |
               +-- ExecutionLoader --+
                                     +-- FileLoader
                                     +-- SourceLoader

class importlib.abc.MetaPathFinder

  An abstract base class representing a meta path finder.

  Added in version 3.3.

  Changed in version 3.10: No longer a subclass of `Finder`.

  find_spec(fullname, path, target=None)

    An abstract method for finding a spec for the specified module. If this is a top-level import, path will be `None`. Otherwise, this is a search for a subpackage or module and path will be the value of `__path__` from the parent package. If a spec cannot be found, `None` is returned. When passed in, `target` is a module object that the finder may use to make a more educated guess about what spec to return. `importlib.util.spec_from_loader()` may be useful for implementing concrete `MetaPathFinders`.

    Added in version 3.4.

  invalidate_caches()

    An optional method which, when called, should invalidate any internal cache used by the finder. Used by `importlib.invalidate_caches()` when invalidating the caches of all finders on `sys.meta_path`.

    Changed in version 3.4: Returns `None` when called instead of `NotImplemented`.

class importlib.abc.PathEntryFinder

  An abstract base class representing a path entry finder. Though it bears some similarities to `MetaPathFinder`, `PathEntryFinder` is meant for use only within the path-based import subsystem provided by `importlib.machinery.PathFinder`.

  Added in version 3.3.

  Changed in version 3.10: No longer a subclass of `Finder`.

  find_spec(fullname, target=None)

    An abstract method for finding a spec for the specified module. The finder will search for the module only within the path entry to which it is assigned. If a spec cannot be found, `None` is returned. When passed in, `target` is a module object that the finder may use to make a more educated guess about what spec to return. `importlib.util.spec_from_loader()` may be useful for implementing concrete `PathEntryFinders`.

    Added in version 3.4.

  invalidate_caches()

    An optional method which, when called, should invalidate any internal cache used by the finder. Used by `importlib.machinery.PathFinder.invalidate_caches()` when invalidating the caches of all cached finders.

class importlib.abc.Loader

  An abstract base class for a loader. See PEP 302 for the exact definition for a loader.

  Loaders that wish to support resource reading should implement a `get_resource_reader()` method as specified by `importlib.resources.abc.ResourceReader`.

  Changed in version 3.7: Introduced the optional `get_resource_reader()` method.

  create_module(spec)

    A method that returns the module object to use when importing a module. This method may return `None`, indicating that default module creation semantics should take place.

    Added in version 3.4.

    Changed in version 3.6: This method is no longer optional when `exec_module()` is defined.

  exec_module(module)

    An abstract method that executes the module in its own namespace when a module is imported or reloaded. The module should already be initialized when `exec_module()` is called. When this method exists, `create_module()` must be defined.

    Added in version 3.4.

    Changed in version 3.6: `create_module()` must also be defined.

  load_module(fullname)

    A legacy method for loading a module. If the module cannot be loaded, `ImportError` is raised, otherwise the loaded module is returned.

    If the requested module already exists in `sys.modules`, that module should be used and reloaded. Otherwise the loader should create a new module and insert it into `sys.modules` before any loading begins, to prevent recursion from the import. If the loader inserted a module and the load fails, it must be removed by the loader from `sys.modules`; modules already in `sys.modules` before the loader began execution should be left alone.

    The loader should set several attributes on the module (note that some of these attributes can change when a module is reloaded):

    - `__name__`

        The module’s fully qualified name. It is `'__main__'` for an executed module.

    - `__file__`

        The location the loader used to load the module. For example, for modules loaded from a .py file this is the filename. It is not set on all modules (e.g. built-in modules).

    - `__cached__`

        The filename of a compiled version of the module’s code. It is not set on all modules (e.g. built-in modules).

    - `__path__`

        The list of locations where the package’s submodules will be found. Most of the time this is a single directory. The import system passes this attribute to `__import__()` and to finders in the same way as `sys.path` but just for the package. It is not set on non-package modules so it can be used as an indicator that the module is a package.

    - `__package__`

        The fully qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as `__name__`.

    - `__loader__`

        The loader used to load the module.

    When `exec_module()` is available then backwards-compatible functionality is provided.

    Changed in version 3.4: Raise `ImportError` when called instead of `NotImplementedError`. Functionality provided when `exec_module()` is available.

    Deprecated since version 3.4: The recommended API for loading a module is `exec_module()` (and `create_module()`). Loaders should implement it instead of `load_module()`. The import machinery takes care of all the other responsibilities of `load_module()` when `exec_module()` is implemented.

class importlib.abc.ResourceLoader

  An abstract base class for a loader which implements the optional PEP 302 protocol for loading arbitrary resources from the storage back-end.

  Deprecated since version 3.7: This ABC is deprecated in favour of supporting resource loading through `importlib.resources.abc.ResourceReader`.

  abstractmethod get_data(path)

    An abstract method to return the bytes for the data located at path. Loaders that have a file-like storage back-end that allows storing arbitrary data can implement this abstract method to give direct access to the data stored. `OSError` is to be raised if the path cannot be found. The path is expected to be constructed using a module’s `__file__` attribute or an item from a package’s `__path__`.

    Changed in version 3.4: Raises `OSError` instead of `NotImplementedError`.

class importlib.abc.InspectLoader

  An abstract base class for a loader which implements the optional PEP 302 protocol for loaders that inspect modules.

  get_code(fullname)

    Return the code object for a module, or `None` if the module does not have a code object (as would be the case, for example, for a built-in module). Raise an `ImportError` if loader cannot find the requested module.

    Note

    While the method has a default implementation, it is suggested that it be overridden if possible for performance.

    Changed in version 3.4: No longer abstract and a concrete implementation is provided.

  abstractmethod get_source(fullname)

    An abstract method to return the source of a module. It is returned as a text string using universal newlines, translating all recognized line separators into `'\n'` characters. Returns `None` if no source is available (e.g. a built-in module). Raises `ImportError` if the loader cannot find the module specified.

    Changed in version 3.4: Raises `ImportError` instead of `NotImplementedError`.

  is_package(fullname)

    An optional method to return a true value if the module is a package, a false value otherwise. `ImportError` is raised if the loader cannot find the module.

    Changed in version 3.4: Raises `ImportError` instead of `NotImplementedError`.

  static source_to_code(data, path='<string>')

    Create a code object from Python source.

    The data argument can be whatever the `compile()` function supports (i.e. string or bytes). The path argument should be the “path” to where the source code originated from, which can be an abstract concept (e.g. location in a zip file).

    With the subsequent code object one can execute it in a module by running `exec(code, module.__dict__)`.

    Added in version 3.4.

    Changed in version 3.5: Made the method static.

  exec_module(module)

    Implementation of `Loader.exec_module()`.

    Added in version 3.4.

  load_module(fullname)

    Implementation of `Loader.load_module()`.

    Deprecated since version 3.4: use `exec_module()` instead.

class importlib.abc.ExecutionLoader

  An abstract base class which inherits from `InspectLoader` that, when implemented, helps a module to be executed as a script. The ABC represents an optional PEP 302 protocol.

  abstractmethod get_filename(fullname)

    An abstract method that is to return the value of `__file__` for the specified module. If no path is available, `ImportError` is raised.

    If source code is available, then the method should return the path to the source file, regardless of whether a bytecode was used to load the module.

    Changed in version 3.4: Raises `ImportError` instead of `NotImplementedError`.

class importlib.abc.FileLoader(fullname, path)

  An abstract base class which inherits from `ResourceLoader` and `ExecutionLoader`, providing concrete implementations of `ResourceLoader.get_data()` and `ExecutionLoader.get_filename()`.

  The fullname argument is a fully resolved name of the module the loader is to handle. The path argument is the path to the file for the module.

  Added in version 3.3.

  name

    The name of the module the loader can handle.

  path

    Path to the file of the module.

  load_module(fullname)

    Calls super’s `load_module()`.

    Deprecated since version 3.4: Use `Loader.exec_module()` instead.

  abstractmethod get_filename(fullname)

    Returns `path`.

  abstractmethod get_data(path)

    Reads path as a binary file and returns the bytes from it.

class importlib.abc.SourceLoader

  An abstract base class for implementing source (and optionally bytecode) file loading. The class inherits from both `ResourceLoader` and `ExecutionLoader`, requiring the implementation of:

  - `ResourceLoader.get_data()`

  - `ExecutionLoader.get_filename()`

      Should only return the path to the source file; sourceless loading is not supported.

  The abstract methods defined by this class are to add optional bytecode file support. Not implementing these optional methods (or causing them to raise `NotImplementedError`) causes the loader to only work with source code. Implementing the methods allows the loader to work with source and bytecode files; it does not allow for sourceless loading where only bytecode is provided. Bytecode files are an optimization to speed up loading by removing the parsing step of Python’s compiler, and so no bytecode-specific API is exposed.

  path_stats(path)

    Optional abstract method which returns a `dict` containing metadata about the specified path. Supported dictionary keys are:

    - `'mtime'` (mandatory): an integer or floating-point number representing the modification time of the source code;

    - `'size'` (optional): the size in bytes of the source code.

    Any other keys in the dictionary are ignored, to allow for future extensions. If the path cannot be handled, `OSError` is raised.

    Added in version 3.3.

    Changed in version 3.4: Raise `OSError` instead of `NotImplementedError`.

  path_mtime(path)

    Optional abstract method which returns the modification time for the specified path.

    Deprecated since version 3.3: This method is deprecated in favour of `path_stats()`. You don’t have to implement it, but it is still available for compatibility purposes. Raise `OSError` if the path cannot be handled.

    Changed in version 3.4: Raise `OSError` instead of `NotImplementedError`.

  set_data(path, data)

    Optional abstract method which writes the specified bytes to a file path. Any intermediate directories which do not exist are to be created automatically.

    When writing to the path fails because the path is read-only (`errno.EACCES`/`PermissionError`), do not propagate the exception.

    Changed in version 3.4: No longer raises `NotImplementedError` when called.

  get_code(fullname)

    Concrete implementation of `InspectLoader.get_code()`.

  exec_module(module)

    Concrete implementation of `Loader.exec_module()`.

    Added in version 3.4.

  load_module(fullname)

    Concrete implementation of `Loader.load_module()`.

    Deprecated since version 3.4: Use `exec_module()` instead.

  get_source(fullname)

    Concrete implementation of `InspectLoader.get_source()`.

  is_package(fullname)

    Concrete implementation of `InspectLoader.is_package()`. A module is determined to be a package if its file path (as provided by `ExecutionLoader.get_filename()`) is a file named `__init__` when the file extension is removed and the module name itself does not end in `__init__`.

class importlib.abc.ResourceReader

  Superseded by TraversableResources

  An abstract base class to provide the ability to read resources.

  From the perspective of this ABC, a resource is a binary artifact that is shipped within a package. Typically this is something like a data file that lives next to the `__init__.py` file of the package. The purpose of this class is to help abstract out the accessing of such data files so that it does not matter if the package and its data file(s) are stored in a e.g. zip file versus on the file system.

  For any of methods of this class, a resource argument is expected to be a path-like object which represents conceptually just a file name. This means that no subdirectory paths should be included in the resource argument. This is because the location of the package the reader is for, acts as the “directory”. Hence the metaphor for directories and file names is packages and resources, respectively. This is also why instances of this class are expected to directly correlate to a specific package (instead of potentially representing multiple packages or a module).

  Loaders that wish to support resource reading are expected to provide a method called `get_resource_reader(fullname)` which returns an object implementing this ABC’s interface. If the module specified by fullname is not a package, this method should return `None`. An object compatible with this ABC should only be returned when the specified module is a package.

  Added in version 3.7.

  Deprecated since version 3.12, will be removed in version 3.14: Use `importlib.resources.abc.TraversableResources` instead.

  abstractmethod open_resource(resource)

    Returns an opened, file-like object for binary reading of the resource.

    If the resource cannot be found, `FileNotFoundError` is raised.

  abstractmethod resource_path(resource)

    Returns the file system path to the resource.

    If the resource does not concretely exist on the file system, raise `FileNotFoundError`.

  abstractmethod is_resource(name)

    Returns `True` if the named name is considered a resource. `FileNotFoundError` is raised if name does not exist.

  abstractmethod contents()

    Returns an iterable of strings over the contents of the package. Do note that it is not required that all names returned by the iterator be actual resources, e.g. it is acceptable to return names for which `is_resource()` would be false.

    Allowing non-resource names to be returned is to allow for situations where how a package and its resources are stored are known a priori and the non-resource names would be useful. For instance, returning subdirectory names is allowed so that when it is known that the package and resources are stored on the file system then those subdirectory names can be used directly.

    The abstract method returns an iterable of no items.

class importlib.abc.Traversable

  An object with a subset of `pathlib.Path` methods suitable for traversing directories and opening files.

  For a representation of the object on the file-system, use `importlib.resources.as_file()`.

  Added in version 3.9.

  Deprecated since version 3.12, will be removed in version 3.14: Use `importlib.resources.abc.Traversable` instead.

  name

    Abstract. The base name of this object without any parent references.

  abstractmethod iterdir()

    Yield `Traversable` objects in `self`.

  abstractmethod is_dir()

    Return `True` if `self` is a directory.

  abstractmethod is_file()

    Return `True` if `self` is a file.

  abstractmethod joinpath(child)

    Return Traversable child in `self`.

  abstractmethod __truediv__(child)

    Return `Traversable` child in `self`.

  abstractmethod open(mode='r', *args, **kwargs)

    mode may be ‘r’ or ‘rb’ to open as text or binary. Return a handle suitable for reading (same as `pathlib.Path.open`).

    When opening as text, accepts encoding parameters such as those accepted by `io.TextIOWrapper`.

  read_bytes()

    Read contents of `self` as bytes.

  read_text(encoding=None)

    Read contents of `self` as text.

class importlib.abc.TraversableResources

  An abstract base class for resource readers capable of serving the `importlib.resources.files()` interface. Subclasses `importlib.resources.abc.ResourceReader` and provides concrete implementations of the `importlib.resources.abc.ResourceReader`’s abstract methods. Therefore, any loader supplying `importlib.abc.TraversableResources` also supplies ResourceReader.

  Loaders that wish to support resource reading are expected to implement this interface.

  Added in version 3.9.

  Deprecated since version 3.12, will be removed in version 3.14: Use `importlib.resources.abc.TraversableResources` instead.

  abstractmethod files()

    Returns a `importlib.resources.abc.Traversable` object for the loaded package.

## `importlib.machinery` – Importers and path hooks

Source code: Lib/importlib/machinery.py

This module contains the various objects that help `import` find and load modules.

importlib.machinery.SOURCE_SUFFIXES

  A list of strings representing the recognized file suffixes for source modules.

  Added in version 3.3.

importlib.machinery.DEBUG_BYTECODE_SUFFIXES

  A list of strings representing the file suffixes for non-optimized bytecode modules.

  Added in version 3.3.

  Deprecated since version 3.5: Use `BYTECODE_SUFFIXES` instead.

importlib.machinery.OPTIMIZED_BYTECODE_SUFFIXES

  A list of strings representing the file suffixes for optimized bytecode modules.

  Added in version 3.3.

  Deprecated since version 3.5: Use `BYTECODE_SUFFIXES` instead.

importlib.machinery.BYTECODE_SUFFIXES

  A list of strings representing the recognized file suffixes for bytecode modules (including the leading dot).

  Added in version 3.3.

  Changed in version 3.5: The value is no longer dependent on `__debug__`.

importlib.machinery.EXTENSION_SUFFIXES

  A list of strings representing the recognized file suffixes for extension modules.

  Added in version 3.3.

importlib.machinery.all_suffixes()

  Returns a combined list of strings representing all file suffixes for modules recognized by the standard import machinery. This is a helper for code which simply needs to know if a filesystem path potentially refers to a module without needing any details on the kind of module (for example, `inspect.getmodulename()`).

  Added in version 3.3.

class importlib.machinery.BuiltinImporter

  An importer for built-in modules. All known built-in modules are listed in `sys.builtin_module_names`. This class implements the `importlib.abc.MetaPathFinder` and `importlib.abc.InspectLoader` ABCs.

  Only class methods are defined by this class to alleviate the need for instantiation.

  Changed in version 3.5: As part of PEP 489, the builtin importer now implements `Loader.create_module()` and `Loader.exec_module()`

class importlib.machinery.FrozenImporter

  An importer for frozen modules. This class implements the `importlib.abc.MetaPathFinder` and `importlib.abc.InspectLoader` ABCs.

  Only class methods are defined by this class to alleviate the need for instantiation.

  Changed in version 3.4: Gained `create_module()` and `exec_module()` methods.

class importlib.machinery.WindowsRegistryFinder

  Finder for modules declared in the Windows registry. This class implements the `importlib.abc.MetaPathFinder` ABC.

  Only class methods are defined by this class to alleviate the need for instantiation.

  Added in version 3.3.

  Deprecated since version 3.6: Use `site` configuration instead. Future versions of Python may not enable this finder by default.

class importlib.machinery.PathFinder

  A Finder for `sys.path` and package `__path__` attributes. This class implements the `importlib.abc.MetaPathFinder` ABC.

  Only class methods are defined by this class to alleviate the need for instantiation.

  classmethod find_spec(fullname, path=None, target=None)

    Class method that attempts to find a spec for the module specified by fullname on `sys.path` or, if defined, on path. For each path entry that is searched, `sys.path_importer_cache` is checked. If a non-false object is found then it is used as the path entry finder to look for the module being searched for. If no entry is found in `sys.path_importer_cache`, then `sys.path_hooks` is searched for a finder for the path entry and, if found, is stored in `sys.path_importer_cache` along with being queried about the module. If no finder is ever found then `None` is both stored in the cache and returned.

    Added in version 3.4.

    Changed in version 3.5: If the current working directory – represented by an empty string – is no longer valid then `None` is returned but no value is cached in `sys.path_importer_cache`.

  classmethod invalidate_caches()

    Calls `importlib.abc.PathEntryFinder.invalidate_caches()` on all finders stored in `sys.path_importer_cache` that define the method. Otherwise entries in `sys.path_importer_cache` set to `None` are deleted.

    Changed in version 3.7: Entries of `None` in `sys.path_importer_cache` are deleted.

  Changed in version 3.4: Calls objects in `sys.path_hooks` with the current working directory for `''` (i.e. the empty string).

class importlib.machinery.FileFinder(path, *loader_details)

  A concrete implementation of `importlib.abc.PathEntryFinder` which caches results from the file system.

  The path argument is the directory for which the finder is in charge of searching.

  The loader_details argument is a variable number of 2-item tuples each containing a loader and a sequence of file suffixes the loader recognizes. The loaders are expected to be callables which accept two arguments of the module’s name and the path to the file found.

  The finder will cache the directory contents as necessary, making stat calls for each module search to verify the cache is not outdated. Because cache staleness relies upon the granularity of the operating system’s state information of the file system, there is a potential race condition of searching for a module, creating a new file, and then searching for the module the new file represents. If the operations happen fast enough to fit within the granularity of stat calls, then the module search will fail. To prevent this from happening, when you create a module dynamically, make sure to call `importlib.invalidate_caches()`.

  Added in version 3.3.

  path

    The path the finder will search in.

  find_spec(fullname, target=None)

    Attempt to find the spec to handle fullname within `path`.

    Added in version 3.4.

  invalidate_caches()

    Clear out the internal cache.

  classmethod path_hook(*loader_details)

    A class method which returns a closure for use on `sys.path_hooks`. An instance of `FileFinder` is returned by the closure using the path argument given to the closure directly and loader_details indirectly.

    If the argument to the closure is not an existing directory, `ImportError` is raised.

class importlib.machinery.SourceFileLoader(fullname, path)

  A concrete implementation of `importlib.abc.SourceLoader` by subclassing `importlib.abc.FileLoader` and providing some concrete implementations of other methods.

  Added in version 3.3.

  name

    The name of the module that this loader will handle.

  path

    The path to the source file.

  is_package(fullname)

    Return `True` if `path` appears to be for a package.

  path_stats(path)

    Concrete implementation of `importlib.abc.SourceLoader.path_stats()`.

  set_data(path, data)

    Concrete implementation of `importlib.abc.SourceLoader.set_data()`.

  load_module(name=None)

    Concrete implementation of `importlib.abc.Loader.load_module()` where specifying the name of the module to load is optional.

    Deprecated since version 3.6: Use `importlib.abc.Loader.exec_module()` instead.

class importlib.machinery.SourcelessFileLoader(fullname, path)

  A concrete implementation of `importlib.abc.FileLoader` which can import bytecode files (i.e. no source code files exist).

  Please note that direct use of bytecode files (and thus not source code files) inhibits your modules from being usable by all Python implementations or new versions of Python which change the bytecode format.

  Added in version 3.3.

  name

    The name of the module the loader will handle.

  path

    The path to the bytecode file.

  is_package(fullname)

    Determines if the module is a package based on `path`.

  get_code(fullname)

    Returns the code object for `name` created from `path`.

  get_source(fullname)

    Returns `None` as bytecode files have no source when this loader is used.

  load_module(name=None)

  Concrete implementation of `importlib.abc.Loader.load_module()` where specifying the name of the module to load is optional.

  Deprecated since version 3.6: Use `importlib.abc.Loader.exec_module()` instead.

class importlib.machinery.ExtensionFileLoader(fullname, path)

  A concrete implementation of `importlib.abc.ExecutionLoader` for extension modules.

  The fullname argument specifies the name of the module the loader is to support. The path argument is the path to the extension module’s file.

  Note that, by default, importing an extension module will fail in subinterpreters if it doesn’t implement multi-phase init (see PEP 489), even if it would otherwise import successfully.

  Added in version 3.3.

  Changed in version 3.12: Multi-phase init is now required for use in subinterpreters.

  name

    Name of the module the loader supports.

  path

    Path to the extension module.

  create_module(spec)

    Creates the module object from the given specification in accordance with PEP 489.

    Added in version 3.5.

  exec_module(module)

    Initializes the given module object in accordance with PEP 489.

    Added in version 3.5.

  is_package(fullname)

    Returns `True` if the file path points to a package’s `__init__` module based on `EXTENSION_SUFFIXES`.

  get_code(fullname)

    Returns `None` as extension modules lack a code object.

  get_source(fullname)

    Returns `None` as extension modules do not have source code.

  get_filename(fullname)

    Returns `path`.

    Added in version 3.4.

class importlib.machinery.NamespaceLoader(name, path, path_finder)

  A concrete implementation of `importlib.abc.InspectLoader` for namespace packages. This is an alias for a private class and is only made public for introspecting the `__loader__` attribute on namespace packages:

      >>> from importlib.machinery import NamespaceLoader
      >>> import my_namespace
      >>> isinstance(my_namespace.__loader__, NamespaceLoader)
      True
      >>> import importlib.abc
      >>> isinstance(my_namespace.__loader__, importlib.abc.Loader)
      True

  Added in version 3.11.

class importlib.machinery.ModuleSpec(name, loader, *, origin=None, loader_state=None, is_package=None)

  A specification for a module’s import-system-related state. This is typically exposed as the module’s `__spec__` attribute. In the descriptions below, the names in parentheses give the corresponding attribute available directly on the module object, e.g. `module.__spec__.origin == module.__file__`. Note, however, that while the values are usually equivalent, they can differ since there is no synchronization between the two objects. For example, it is possible to update the module’s `__file__` at runtime and this will not be automatically reflected in the module’s `__spec__.origin`, and vice versa.

  Added in version 3.4.

  name

  (`__name__`)

  The module’s fully qualified name. The finder should always set this attribute to a non-empty string.

  loader

  (`__loader__`)

  The loader used to load the module. The finder should always set this attribute.

  origin

  (`__file__`)

  The location the loader should use to load the module. For example, for modules loaded from a .py file this is the filename. The finder should always set this attribute to a meaningful value for the loader to use. In the uncommon case that there is not one (like for namespace packages), it should be set to `None`.

  submodule_search_locations

  (`__path__`)

  The list of locations where the package’s submodules will be found. Most of the time this is a single directory. The finder should set this attribute to a list, even an empty one, to indicate to the import system that the module is a package. It should be set to `None` for non-package modules. It is set automatically later to a special object for namespace packages.

  loader_state

  The finder may set this attribute to an object containing additional, module-specific data to use when loading the module. Otherwise it should be set to `None`.

  cached

  (`__cached__`)

  The filename of a compiled version of the module’s code. The finder should always set this attribute but it may be `None` for modules that do not need compiled code stored.

  parent

  (`__package__`)

  (Read-only) The fully qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as `name`.

  has_location
  `True` if the spec’s `origin` refers to a loadable location,

    `False` otherwise. This value impacts how `origin` is interpreted and how the module’s `__file__` is populated.

## `importlib.util` – Utility code for importers

Source code: Lib/importlib/util.py

This module contains the various objects that help in the construction of an importer.

importlib.util.MAGIC_NUMBER

  The bytes which represent the bytecode version number. If you need help with loading/writing bytecode then consider `importlib.abc.SourceLoader`.

  Added in version 3.4.

importlib.util.cache_from_source(path, debug_override=None, *, optimization=None)

  Return the PEP 3147/PEP 488 path to the byte-compiled file associated with the source path. For example, if path is `/foo/bar/baz.py` the return value would be `/foo/bar/__pycache__/baz.cpython-32.pyc` for Python 3.2. The `cpython-32` string comes from the current magic tag (see `get_tag()`; if `sys.implementation.cache_tag` is not defined then `NotImplementedError` will be raised).

  The optimization parameter is used to specify the optimization level of the bytecode file. An empty string represents no optimization, so `/foo/bar/baz.py` with an optimization of `''` will result in a bytecode path of `/foo/bar/__pycache__/baz.cpython-32.pyc`. `None` causes the interpreter’s optimization level to be used. Any other value’s string representation is used, so `/foo/bar/baz.py` with an optimization of `2` will lead to the bytecode path of `/foo/bar/__pycache__/baz.cpython-32.opt-2.pyc`. The string representation of optimization can only be alphanumeric, else `ValueError` is raised.

  The debug_override parameter is deprecated and can be used to override the system’s value for `__debug__`. A `True` value is the equivalent of setting optimization to the empty string. A `False` value is the same as setting optimization to `1`. If both debug_override an optimization are not `None` then `TypeError` is raised.

  Added in version 3.4.

  Changed in version 3.5: The optimization parameter was added and the debug_override parameter was deprecated.

  Changed in version 3.6: Accepts a path-like object.

importlib.util.source_from_cache(path)

  Given the path to a PEP 3147 file name, return the associated source code file path. For example, if path is `/foo/bar/__pycache__/baz.cpython-32.pyc` the returned path would be `/foo/bar/baz.py`. path need not exist, however if it does not conform to PEP 3147 or PEP 488 format, a `ValueError` is raised. If `sys.implementation.cache_tag` is not defined, `NotImplementedError` is raised.

  Added in version 3.4.

  Changed in version 3.6: Accepts a path-like object.

importlib.util.decode_source(source_bytes)

  Decode the given bytes representing source code and return it as a string with universal newlines (as required by `importlib.abc.InspectLoader.get_source()`).

  Added in version 3.4.

importlib.util.resolve_name(name, package)

  Resolve a relative module name to an absolute one.

  If name has no leading dots, then name is simply returned. This allows for usage such as `importlib.util.resolve_name('sys', __spec__.parent)` without doing a check to see if the package argument is needed.

  `ImportError` is raised if name is a relative module name but package is a false value (e.g. `None` or the empty string). `ImportError` is also raised if a relative name would escape its containing package (e.g. requesting `..bacon` from within the `spam` package).

  Added in version 3.3.

  Changed in version 3.9: To improve consistency with import statements, raise `ImportError` instead of `ValueError` for invalid relative import attempts.

importlib.util.find_spec(name, package=None)

  Find the spec for a module, optionally relative to the specified package name. If the module is in `sys.modules`, then `sys.modules[name].__spec__` is returned (unless the spec would be `None` or is not set, in which case `ValueError` is raised). Otherwise a search using `sys.meta_path` is done. `None` is returned if no spec is found.

  If name is for a submodule (contains a dot), the parent module is automatically imported.

  name and package work the same as for `import_module()`.

  Added in version 3.4.

  Changed in version 3.7: Raises `ModuleNotFoundError` instead of `AttributeError` if package is in fact not a package (i.e. lacks a `__path__` attribute).

importlib.util.module_from_spec(spec)

  Create a new module based on spec and `spec.loader.create_module`.

  If `spec.loader.create_module` does not return `None`, then any pre-existing attributes will not be reset. Also, no `AttributeError` will be raised if triggered while accessing spec or setting an attribute on the module.

  This function is preferred over using `types.ModuleType` to create a new module as spec is used to set as many import-controlled attributes on the module as possible.

  Added in version 3.5.

importlib.util.spec_from_loader(name, loader, *, origin=None, is_package=None)

  A factory function for creating a `ModuleSpec` instance based on a loader. The parameters have the same meaning as they do for ModuleSpec. The function uses available loader APIs, such as `InspectLoader.is_package()`, to fill in any missing information on the spec.

  Added in version 3.4.

importlib.util.spec_from_file_location(name, location, *, loader=None, submodule_search_locations=None)

  A factory function for creating a `ModuleSpec` instance based on the path to a file. Missing information will be filled in on the spec by making use of loader APIs and by the implication that the module will be file-based.

  Added in version 3.4.

  Changed in version 3.6: Accepts a path-like object.

importlib.util.source_hash(source_bytes)

  Return the hash of source_bytes as bytes. A hash-based `.pyc` file embeds the `source_hash()` of the corresponding source file’s contents in its header.

  Added in version 3.7.

importlib.util._incompatible_extension_module_restrictions(*, disable_check)

  A context manager that can temporarily skip the compatibility check for extension modules. By default the check is enabled and will fail when a single-phase init module is imported in a subinterpreter. It will also fail for a multi-phase init module that doesn’t explicitly support a per-interpreter GIL, when imported in an interpreter with its own GIL.

  Note that this function is meant to accommodate an unusual case; one which is likely to eventually go away. There’s is a pretty good chance this is not what you were looking for.

  You can get the same effect as this function by implementing the basic interface of multi-phase init (PEP 489) and lying about support for multiple interpreters (or per-interpreter GIL).

  Warning

  Using this function to disable the check can lead to unexpected behavior and even crashes. It should only be used during extension module development.

  Added in version 3.12.

class importlib.util.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 `exec_module()` as control over what module type is used for the module is required. For those same reasons, the loader’s `create_module()` method must return `None` or a type for which its `__class__` attribute can be mutated along with not using slots. Finally, modules which substitute the object placed into `sys.modules` will not work as there is no way to properly replace the module references throughout the interpreter safely; `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.

  Added in version 3.5.

  Changed in version 3.6: Began calling `create_module()`, removing the compatibility warning for `importlib.machinery.BuiltinImporter` and `importlib.machinery.ExtensionFileLoader`.

  classmethod factory(loader)

    A class 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))

## Examples

### Importing programmatically

To programmatically import a module, use `importlib.import_module()`.

    import importlib

    itertools = importlib.import_module('itertools')

### Checking if a module can be imported

If you need to find out if a module can be imported without actually doing the import, then you should use `importlib.util.find_spec()`.

Note that if `name` is a submodule (contains a dot), `importlib.util.find_spec()` will import the parent module.

    import importlib.util
    import sys

    # For illustrative purposes.
    name = 'itertools'

    if name in sys.modules:
        print(f"{name!r} already in sys.modules")
    elif (spec := importlib.util.find_spec(name)) is not None:
        # If you chose to perform the actual import ...
        module = importlib.util.module_from_spec(spec)
        sys.modules[name] = module
        spec.loader.exec_module(module)
        print(f"{name!r} has been imported")
    else:
        print(f"can't find the {name!r} module")

### Importing a source file directly

To import a Python source file directly, use the following recipe:

    import importlib.util
    import sys

    # For illustrative purposes.
    import tokenize
    file_path = tokenize.__file__
    module_name = tokenize.__name__

    spec = importlib.util.spec_from_file_location(module_name, file_path)
    module = importlib.util.module_from_spec(spec)
    sys.modules[module_name] = module
    spec.loader.exec_module(module)

### Implementing lazy imports

The example below shows how to implement lazy imports:

    >>> import importlib.util
    >>> import sys
    >>> def lazy_import(name):
    ...     spec = importlib.util.find_spec(name)
    ...     loader = importlib.util.LazyLoader(spec.loader)
    ...     spec.loader = loader
    ...     module = importlib.util.module_from_spec(spec)
    ...     sys.modules[name] = module
    ...     loader.exec_module(module)
    ...     return module
    ...
    >>> lazy_typing = lazy_import("typing")
    >>> #lazy_typing is a real module object,
    >>> #but it is not loaded in memory yet.
    >>> lazy_typing.TYPE_CHECKING
    False

### Setting up an importer

For deep customizations of import, you typically want to implement an importer. This means managing both the finder and loader side of things. For finders there are two flavours to choose from depending on your needs: a meta path finder or a path entry finder. The former is what you would put on `sys.meta_path` while the latter is what you create using a path entry hook on `sys.path_hooks` which works with `sys.path` entries to potentially create a finder. This example will show you how to register your own importers so that import will use them (for creating an importer for yourself, read the documentation for the appropriate classes defined within this package):

    import importlib.machinery
    import sys

    # For illustrative purposes only.
    SpamMetaPathFinder = importlib.machinery.PathFinder
    SpamPathEntryFinder = importlib.machinery.FileFinder
    loader_details = (importlib.machinery.SourceFileLoader,
                      importlib.machinery.SOURCE_SUFFIXES)

    # Setting up a meta path finder.
    # Make sure to put the finder in the proper location in the list in terms of
    # priority.
    sys.meta_path.append(SpamMetaPathFinder)

    # Setting up a path entry finder.
    # Make sure to put the path hook in the proper location in the list in terms
    # of priority.
    sys.path_hooks.append(SpamPathEntryFinder.path_hook(loader_details))

### Approximating `importlib.import_module()`

Import itself is implemented in Python code, making it possible to expose most of the import machinery through importlib. The following helps illustrate the various APIs that importlib exposes by providing an approximate implementation of `importlib.import_module()`:

    import importlib.util
    import sys

    def import_module(name, package=None):
        """An approximate implementation of import."""
        absolute_name = importlib.util.resolve_name(name, package)
        try:
            return sys.modules[absolute_name]
        except KeyError:
            pass

        path = None
        if '.' in absolute_name:
            parent_name, _, child_name = absolute_name.rpartition('.')
            parent_module = import_module(parent_name)
            path = parent_module.__spec__.submodule_search_locations
        for finder in sys.meta_path:
            spec = finder.find_spec(absolute_name, path)
            if spec is not None:
                break
        else:
            msg = f'No module named {absolute_name!r}'
            raise ModuleNotFoundError(msg, name=absolute_name)
        module = importlib.util.module_from_spec(spec)
        sys.modules[absolute_name] = module
        spec.loader.exec_module(module)
        if path is not None:
            setattr(parent_module, child_name, module)
        return module