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

多階段擴充模組初始化

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.

警告

This function is not thread-safe. Calling it from multiple threads can result in unexpected behavior. It's recommended to use the threading.Lock or other synchronization primitives for thread-safe module reloading.

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: 不再是 Finder 的子類別。

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: 呼叫時回傳 None 而非 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: 不再是 Finder 的子類別。

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.

自從版本 3.4 後不推薦使用，將會自版本 3.15 中移除。: 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

Superseded by TraversableResources

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.TraversableResources. This class exists for backwards compatibility only with other ABCs in this module.

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: 引發 OSError 而非 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: 引發 ImportError 而非 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: 引發 ImportError 而非 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。

自從版本 3.4 後不推薦使用，將會自版本 3.15 中移除。: 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: 引發 ImportError 而非 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().

自從版本 3.4 後不推薦使用，將會自版本 3.15 中移除。: 改用 Loader.exec_module()。

abstractmethod get_filename(fullname)

回傳 path。

abstractmethod get_data(path)

將 path 作為二進位檔案讀取並回傳其位元組。

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: 引發 OSError 而非 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: 引發 OSError 而非 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: 呼叫時不再引發 NotImplementedError。

get_code(fullname)

InspectLoader.get_code() 的具體實作。

exec_module(module)

Loader.exec_module() 的具體實作。

在 3.4 版被加入.

load_module(fullname)

Loader.load_module() 的具體實作。

自從版本 3.4 後不推薦使用，將會自版本 3.15 中移除。: 改用 exec_module()。

get_source(fullname)

InspectLoader.get_source() 的具體實作。

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__.

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: 改用 BYTECODE_SUFFIXES。

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: 改用 BYTECODE_SUFFIXES。

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.