importlib --- import 的實作

在 3.1 版被加入.

原始碼：Lib/importlib/__init__.py

簡介

importlib 的目的可分為三個部分。

第一是提供 Python 原始碼中 import 陳述式的實作（因此，也延伸到 __import__() 函式）。這讓 import 實作可以移植到任何 Python 直譯器。同時，這也提供了一個比用其他程式語言實作更容易理解的版本。

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:

也參考

import 陳述式

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).

__import__() 函式

The import statement is syntactic sugar for this function.

sys.path 模組搜尋路徑的初始化

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

函式

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

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

備註

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.

在 3.3 版的變更: 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.

在 3.3 版被加入.

在 3.10 版的變更: 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.

在 3.4 版被加入.

在 3.7 版的變更: ModuleNotFoundError is raised when the module being reloaded lacks a ModuleSpec.

importlib.abc -- Abstract base classes related to import

原始碼：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.

在 3.3 版被加入.

在 3.10 版的變更: 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.

在 3.4 版被加入.

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.

在 3.4 版的變更: 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.

在 3.3 版被加入.

在 3.10 版的變更: 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.

在 3.4 版被加入.

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.

在 3.7 版的變更: 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.

在 3.4 版被加入.

在 3.6 版的變更: 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.

在 3.4 版被加入.

在 3.6 版的變更: create_module() 也必須被定義。

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):

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

在 3.4 版的變更: Raise ImportError when called instead of NotImplementedError. Functionality provided when exec_module() is available.

在 3.4 版之後被棄用: 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.

在 3.7 版之後被棄用: 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__.

在 3.4 版的變更: 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.

備註

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

在 3.4 版的變更: 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.

在 3.4 版的變更: 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.

在 3.4 版的變更: 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__).

在 3.4 版被加入.

在 3.5 版的變更: Made the method static.

exec_module(module)

Loader.exec_module() 的實作。

在 3.4 版被加入.

load_module(fullname)

Loader.load_module() 的實作。

在 3.4 版之後被棄用: 請改用 exec_module()。

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.

在 3.4 版的變更: 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.

在 3.3 版被加入.

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().

在 3.4 版之後被棄用: 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:

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.

在 3.3 版被加入.

在 3.4 版的變更: Raise OSError instead of NotImplementedError.

path_mtime(path)

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

在 3.3 版之後被棄用: 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.

在 3.4 版的變更: 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.

在 3.4 版的變更: No longer raises NotImplementedError when called.

get_code(fullname)

Concrete implementation of InspectLoader.get_code().

exec_module(module)

Concrete implementation of Loader.exec_module().

在 3.4 版被加入.

load_module(fullname)

Concrete implementation of Loader.load_module().

在 3.4 版之後被棄用: 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 e.g. in a 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.

在 3.7 版被加入.

Deprecated since version 3.12, 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().

在 3.9 版被加入.

Deprecated since version 3.12, 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.

在 3.9 版被加入.

Deprecated since version 3.12, 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

原始碼：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.

在 3.3 版被加入.

importlib.machinery.DEBUG_BYTECODE_SUFFIXES

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

在 3.3 版被加入.

在 3.5 版之後被棄用: Use BYTECODE_SUFFIXES instead.

importlib.machinery.OPTIMIZED_BYTECODE_SUFFIXES

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

在 3.3 版被加入.

在 3.5 版之後被棄用: Use BYTECODE_SUFFIXES instead.

importlib.machinery.BYTECODE_SUFFIXES

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

在 3.3 版被加入.

在 3.5 版的變更: The value is no longer dependent on __debug__.

importlib.machinery.EXTENSION_SUFFIXES

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

在 3.3 版被加入.

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()).

在 3.3 版被加入.

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.

在 3.5 版的變更: 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.

在 3.4 版的變更: 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.

在 3.3 版被加入.

在 3.6 版之後被棄用: 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.

在 3.4 版被加入.

在 3.5 版的變更: 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.

在 3.7 版的變更: Entries of None in sys.path_importer_cache are deleted.

在 3.4 版的變更: 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().

在 3.3 版被加入.

path

The path the finder will search in.

find_spec(fullname, target=None)

Attempt to find the spec to handle fullname within path.

在 3.4 版被加入.

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.

在 3.3 版被加入.

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.

在 3.6 版之後被棄用: 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.

在 3.3 版被加入.

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.

在 3.6 版之後被棄用: 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.

在 3.3 版被加入.

在 3.12 版的變更: 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.

在 3.5 版被加入.

exec_module(module)

Initializes the given module object in accordance with PEP 489.

在 3.5 版被加入.

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.

在 3.4 版被加入.

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

在 3.11 版被加入.

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. Many of these attributes are also available directly on a module: for example, 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.

在 3.4 版被加入.

name

The module's fully qualified name (see module.__name__). The finder should always set this attribute to a non-empty string.

loader

The loader used to load the module (see module.__loader__). The finder should always set this attribute.

origin

The location the loader should use to load the module (see module.__file__). 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

A (possibly empty) sequence of strings enumerating the locations in which a package's submodules will be found (see module.__path__). Most of the time there will only be a single directory in this list.

The finder should set this attribute to a sequence, 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

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

parent

(Read-only) The fully qualified name of the package the module is in (or the empty string for a top-level module). See module.__package__. 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.

class importlib.machinery.AppleFrameworkLoader(name, path)

A specialization of importlib.machinery.ExtensionFileLoader that is able to load extension modules in Framework format.

For compatibility with the iOS App Store, all binary modules in an iOS app must be dynamic libraries, contained in a framework with appropriate metadata, stored in the Frameworks folder of the packaged app. There can be only a single binary per framework, and there can be no executable binary material outside the Frameworks folder.

To accommodate this requirement, when running on iOS, extension module binaries are not packaged as .so files on sys.path, but as individual standalone frameworks. To discover those frameworks, this loader is be registered against the .fwork file extension, with a .fwork file acting as a placeholder in the original location of the binary on sys.path. The .fwork file contains the path of the actual binary in the Frameworks folder, relative to the app bundle. To allow for resolving a framework-packaged binary back to the original location, the framework is expected to contain a .origin file that contains the location of the .fwork file, relative to the app bundle.

For example, consider the case of an import from foo.bar import _whiz, where _whiz is implemented with the binary module sources/foo/bar/_whiz.abi3.so, with sources being the location registered on sys.path, relative to the application bundle. This module must be distributed as Frameworks/foo.bar._whiz.framework/foo.bar._whiz (creating the framework name from the full import path of the module), with an Info.plist file in the .framework directory identifying the binary as a framework. The foo.bar._whiz module would be represented in the original location with a sources/foo/bar/_whiz.abi3.fwork marker file, containing the path Frameworks/foo.bar._whiz/foo.bar._whiz. The framework would also contain Frameworks/foo.bar._whiz.framework/foo.bar._whiz.origin, containing the path to the .fwork file.

When a module is loaded with this loader, the __file__ for the module will report as the location of the .fwork file. This allows code to use the __file__ of a module as an anchor for file system traversal. However, the spec origin will reference the location of the actual binary in the .framework folder.

The Xcode project building the app is responsible for converting any .so files from wherever they exist in the PYTHONPATH into frameworks in the Frameworks folder (including stripping extensions from the module file, the addition of framework metadata, and signing the resulting framework), and creating the .fwork and .origin files. This will usually be done with a build step in the Xcode project; see the iOS documentation for details on how to construct this build step.

在 3.13 版被加入.

Availability: iOS.

name

Name of the module the loader supports.

path

Path to the .fwork file for the extension module.

importlib.util -- Utility code for importers

原始碼：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.

在 3.4 版被加入.

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.

在 3.4 版被加入.

在 3.5 版的變更: The optimization parameter was added and the debug_override parameter was deprecated.

在 3.6 版的變更: 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.

在 3.4 版被加入.

在 3.6 版的變更: 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()).

在 3.4 版被加入.

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).

在 3.3 版被加入.

在 3.9 版的變更: 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().

在 3.4 版被加入.

在 3.7 版的變更: 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.

在 3.5 版被加入.

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.

在 3.4 版被加入.

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.

在 3.4 版被加入.

在 3.6 版的變更: 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.

在 3.7 版被加入.

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).

警告

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

在 3.12 版被加入.

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.

備註

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.

在 3.5 版被加入.

在 3.6 版的變更: 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))

範例

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

This recipe should be used with caution: it is an approximation of an import statement where the file path is specified directly, rather than sys.path being searched. Alternatives should first be considered first, such as modifying sys.path when a proper module is required, or using runpy.run_path() when the global namespace resulting from running a Python file is appropriate.

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

import importlib.util
import sys


def import_from_path(module_name, file_path):
    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)
    return module


# For illustrative purposes only (use of `json` is arbitrary).
import json
file_path = json.__file__
module_name = json.__name__

# Similar outcome as `import json`.
json = import_from_path(module_name, file_path)

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