31.5. importlib — 实现为 import ¶

31.5.1. Introduction ¶

The purpose of the importlib package is two-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.

31.5.2. Functions ¶

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

An implementation of the built-in __import__() 函数。

注意

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 ).

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.

3.3 版改变： Parent packages are automatically imported.

importlib. find_loader ( name , path=None ) ¶

Find the loader for a module, optionally within the specified path . If the module is in sys.modules , then sys.modules[name].__loader__ is returned (unless the loader would be None or is not set, in which case ValueError is raised). Otherwise a search using sys.meta_path 完成。 None is returned if no loader is found.

A dotted name does not have its parents implicitly imported as that requires loading them and that may not be desired. To properly import a submodule you will need to import all parent packages of the submodule and use the correct argument to path .

3.3 版新增。

3.4 版改变： 若 __loader__ is not set, raise ValueError , just like when the attribute is set to None .

从 3.4 版起弃用： 使用 importlib.util.find_spec() 代替。

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.

3.3 版新增。

importlib. reload ( 模块 ) ¶

Reload a previously imported 模块 . 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 ).

当 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.

3.4 版新增。

31.5.3. importlib.abc – Abstract base classes related to import ¶

源代码： Lib/importlib/abc.py

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
 +-- Finder (deprecated)
 |    +-- MetaPathFinder
 |    +-- PathEntryFinder
 +-- Loader
      +-- ResourceLoader --------+
      +-- InspectLoader          |
           +-- ExecutionLoader --+
                                 +-- FileLoader
                                 +-- SourceLoader
								

class importlib.abc. Finder ¶

An abstract base class representing a finder .

从 3.3 版起弃用： 使用 MetaPathFinder or PathEntryFinder 代替。

abstractmethod find_module ( fullname , path=None ) ¶

An abstract method for finding a loader for the specified module. Originally specified in PEP 302 , this method was meant for use in sys.meta_path and in the path-based import subsystem.

3.4 版改变： 返回 None when called instead of raising NotImplementedError .

class importlib.abc. MetaPathFinder ¶

An abstract base class representing a meta path finder . For compatibility, this is a subclass of Finder .

3.3 版新增。

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 将是 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.

3.4 版新增。

find_module ( fullname , path ) ¶

A legacy method for finding a loader for the specified module. If this is a top-level import, path 将是 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 loader cannot be found, None 被返回。

若 find_spec() is defined, backwards-compatible functionality is provided.

3.4 版改变： 返回 None when called instead of raising NotImplementedError . Can use find_spec() to provide functionality.

从 3.4 版起弃用： 使用 find_spec() 代替。

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 .

3.4 版改变： 返回 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 PathFinder . This ABC is a subclass of Finder for compatibility reasons only.

3.3 版新增。

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 路径条目 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.

3.4 版新增。

find_loader ( fullname ) ¶

A legacy method for finding a loader for the specified module. Returns a 2-tuple of (loader, portion) where portion is a sequence of file system locations contributing to part of a namespace package. The loader may be None while specifying portion to signify the contribution of the file system locations to a namespace package. An empty list can be used for portion to signify the loader is not part of a namespace package. If loader is None and portion is the empty list then no loader or location for a namespace package were found (i.e. failure to find anything for the module).

若 find_spec() is defined then backwards-compatible functionality is provided.

3.4 版改变： 返回 (None, []) instead of raising NotImplementedError . Uses find_spec() when available to provide functionality.

从 3.4 版起弃用： 使用 find_spec() 代替。

find_module ( fullname ) ¶

A concrete implementation of Finder.find_module() which is equivalent to self.find_loader(fullname)[0] .

从 3.4 版起弃用： 使用 find_spec() 代替。

invalidate_caches ( ) ¶

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

class importlib.abc. Loader ¶

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

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.

3.4 版新增。

3.5 版改变： Starting in Python 3.6, this method will not be optional when exec_module() is defined.

exec_module ( 模块 ) ¶

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.

3.4 版新增。

3.6 版改变： 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 (see importlib.util.module_for_loader() ).

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

• __name__

  The name of the module.

• __file__

  The path to where the module data is stored (not set for built-in modules).

• __cached__

  The path to where a compiled version of the module is/should be stored (not set when the attribute would be inappropriate).

• __path__

  A list of strings specifying the search path within a package. This attribute is not set on modules.

• __package__

  The parent package for the module/package. If the module is top-level then it has a value of the empty string. The importlib.util.module_for_loader() decorator can handle the details for __package__ .

• __loader__

  The loader used to load the module. The importlib.util.module_for_loader() decorator can handle the details for __package__ .

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

3.4 版改变： 引发 ImportError when called instead of NotImplementedError . Functionality provided when exec_module() is available.

从 3.4 版起弃用： 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.

module_repr ( 模块 ) ¶

A legacy method which when implemented calculates and returns the given module’s repr, as a string. The module type’s default repr() will use the result of this method as appropriate.

3.3 版新增。

3.4 版改变： Made optional instead of an abstractmethod.

从 3.4 版起弃用： The import machinery now takes care of this automatically.

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.

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__ .

3.4 版改变： 引发 OSError 而不是 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.

注意

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

3.4 版改变： 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 通用换行符 , 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.

3.4 版改变： 引发 ImportError 而不是 NotImplementedError .

is_package ( fullname ) ¶

An abstract 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.

3.4 版改变： 引发 ImportError 而不是 NotImplementedError .

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

Create a code object from Python source.

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__) .

3.4 版新增。

3.5 版改变： Made the method static.

exec_module ( 模块 ) ¶

Implementation of Loader.exec_module() .

3.4 版新增。

load_module ( fullname ) ¶

Implementation of Loader.load_module() .

从 3.4 版起弃用： use exec_module() 代替。

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 协议。

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 被引发。

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.

3.4 版改变： 引发 ImportError 而不是 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() .

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.

3.3 版新增。

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() .

从 3.4 版起弃用： 使用 Loader.exec_module() 代替。

abstractmethod get_filename ( fullname ) ¶

返回 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 被引发。

3.3 版新增。

3.4 版改变： 引发 OSError 而不是 NotImplementedError .

path_mtime ( path ) ¶

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

从 3.3 版起弃用： 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.

3.4 版改变： 引发 OSError 而不是 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.

3.4 版改变： No longer raises NotImplementedError when called.

get_code ( fullname ) ¶

Concrete implementation of InspectLoader.get_code() .

exec_module ( 模块 ) ¶

Concrete implementation of Loader.exec_module() .

3.4 版新增。

load_module ( fullname ) ¶

Concrete implementation of Loader.load_module() .

从 3.4 版起弃用： 使用 exec_module() 代替。

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__ .

31.5.4. importlib.machinery – Importers and path hooks ¶

源代码： 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.

3.3 版新增。

importlib.machinery. DEBUG_BYTECODE_SUFFIXES ¶

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

3.3 版新增。

从 3.5 版起弃用： 使用 BYTECODE_SUFFIXES 代替。

importlib.machinery. OPTIMIZED_BYTECODE_SUFFIXES ¶

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

3.3 版新增。

从 3.5 版起弃用： 使用 BYTECODE_SUFFIXES 代替。

importlib.machinery. BYTECODE_SUFFIXES ¶

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

3.3 版新增。

3.5 版改变： The value is no longer dependent on __debug__ .

importlib.machinery. EXTENSION_SUFFIXES ¶

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

3.3 版新增。

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() ).

3.3 版新增。

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.

3.5 版改变： 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.

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.

3.3 版新增。

从 3.6 版起弃用： 使用 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.

3.4 版新增。

3.5 版改变： 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 find_module ( fullname , path=None ) ¶

A legacy wrapper around find_spec() .

从 3.4 版起弃用： 使用 find_spec() 代替。

classmethod invalidate_caches ( ) ¶

调用 importlib.abc.PathEntryFinder.invalidate_caches() on all finders stored in sys.path_importer_cache .

3.4 版改变： 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.

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

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() .

3.3 版新增。

path ¶

The path the finder will search in.

find_spec ( fullname , target=None ) ¶

Attempt to find the spec to handle fullname within path .

3.4 版新增。

find_loader ( fullname ) ¶

Attempt to find the loader to handle fullname within path .

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 被引发。

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.

3.3 版新增。

name ¶

The name of the module that this loader will handle.

path ¶

The path to the source file.

is_package ( fullname ) ¶

返回 True 若 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.

从 3.6 版起弃用： 使用 importlib.abc.Loader.exec_module() 代替。

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.

3.3 版新增。

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 ) ¶

返回 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.

从 3.6 版起弃用： 使用 importlib.abc.Loader.exec_module() 代替。

class importlib.machinery. ExtensionFileLoader ( fullname , path ) ¶

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

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.

3.3 版新增。

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 .

3.5 版新增。

exec_module ( 模块 ) ¶

Initializes the given module object in accordance with PEP 489 .

3.5 版新增。

is_package ( fullname ) ¶

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

get_code ( fullname ) ¶

返回 None as extension modules lack a code object.

get_source ( fullname ) ¶

返回 None as extension modules do not have source code.

get_filename ( fullname ) ¶

返回 path .

3.4 版新增。

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. Thus it is possible to update the module’s __path__ at runtime, and this will not be automatically reflected in __spec__.submodule_search_locations .

3.4 版新增。

name ¶

( __name__ )

A string for the fully-qualified name of the module.

loader ¶

( __loader__ )

The loader to use for loading. For namespace packages this should be set to None .

origin ¶

( __file__ )

Name of the place from which the module is loaded, e.g. “builtin” for built-in modules and the filename for modules loaded from source. Normally “origin” should be set, but it may be None (the default) which indicates it is unspecified.

submodule_search_locations ¶

( __path__ )

List of strings for where to find submodules, if a package ( None 否则)。

loader_state ¶

Container of extra module-specific data for use during loading (or None ).

cached ¶

( __cached__ )

String for where the compiled module should be stored (or None ).

parent ¶

( __package__ )

(Read-only) Fully-qualified name of the package to which the module belongs as a submodule (or None ).

has_location ¶

Boolean indicating whether or not the module’s “origin” attribute refers to a loadable location.

31.5.5. importlib.util – Utility code for importers ¶

源代码： 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 .

3.4 版新增。

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

返回 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. 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).

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 interpter’s optimization level to be used. Any other value’s string representation being 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 被引发。

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 被引发。

3.4 版新增。

3.5 版改变： optimization parameter was added and the debug_override parameter was deprecated.

3.6 版改变： 接受 像路径对象 .

importlib.util. source_from_cache ( path ) ¶

Given the path 到 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 被引发。

3.4 版新增。

3.6 版改变： 接受 像路径对象 .

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() ).

3.4 版新增。

importlib.util. resolve_name ( name , package ) ¶

Resolve a relative module name to an absolute one.

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

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

3.3 版新增。

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 完成。 None is returned if no spec is found.

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

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

3.4 版新增。

importlib.util. module_from_spec ( spec ) ¶

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

若 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.

3.5 版新增。

@ importlib.util. module_for_loader ¶

A 装饰器 for importlib.abc.Loader.load_module() to handle selecting the proper module object to load with. The decorated method is expected to have a call signature taking two positional arguments (e.g. load_module(self, 模块) ) for which the second argument will be the module object to be used by the loader. Note that the decorator will not work on static methods because of the assumption of two arguments.

The decorated method will take in the name of the module to be loaded as expected for a loader . If the module is not found in sys.modules then a new one is constructed. Regardless of where the module came from, __loader__ 设为 self and __package__ is set based on what importlib.abc.InspectLoader.is_package() returns (if available). These attributes are set unconditionally to support reloading.

If an exception is raised by the decorated method and a module was added to sys.modules , then the module will be removed to prevent a partially initialized module from being in left in sys.modules . If the module was already in sys.modules then it is left alone.

3.3 版改变： __loader__ and __package__ are automatically set (when possible).

3.4 版改变： Set __name__ , __loader__ __package__ unconditionally to support reloading.

从 3.4 版起弃用： The import machinery now directly performs all the functionality provided by this function.

@ importlib.util. set_loader ¶

A 装饰器 for importlib.abc.Loader.load_module() to set the __loader__ attribute on the returned module. If the attribute is already set the decorator does nothing. It is assumed that the first positional argument to the wrapped method (i.e. self ) is what __loader__ should be set to.

3.4 版改变： Set __loader__ if set to None , as if the attribute does not exist.

从 3.4 版起弃用： The import machinery takes care of this automatically.

@ importlib.util. set_package ¶

A 装饰器 for importlib.abc.Loader.load_module() to set the __package__ attribute on the returned module. If __package__ is set and has a value other than None it will not be changed.

从 3.4 版起弃用： The import machinery takes care of this automatically.

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.

3.4 版新增。

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.

3.4 版新增。

3.6 版改变： 接受 像路径对象 .

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.

注意

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.

3.5 版新增。

3.6 版改变： Began calling create_module() , removing the compatibility warning for importlib.machinery.BuiltinImporter and importlib.machinery.ExtensionFileLoader .

classmethod factory ( loader ) ¶

A static method which returns a callable that creates a lazy loader. This is meant to be used in situations where the loader is passed by class instead of by instance.

suffixes = importlib.machinery.SOURCE_SUFFIXES
loader = importlib.machinery.SourceFileLoader
lazy_loader = importlib.util.LazyLoader.factory(loader)
finder = importlib.machinery.FileFinder(path, (lazy_loader, suffixes))
												

31.5.6. Examples ¶

import importlib
itertools = importlib.import_module('itertools')
									

import importlib.util
import sys
# For illustrative purposes.
name = 'itertools'
spec = importlib.util.find_spec(name)
if spec is None:
    print("can't find the itertools module")
else:
    # If you chose to perform the actual import ...
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    # Adding the module to sys.modules is optional.
    sys.modules[name] = module
									

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)
spec.loader.exec_module(module)
# Optional; only necessary if you want to be able to import the module
# by name later.
sys.modules[module_name] = module
									

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))
									

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:
        raise ImportError(f'No module named {absolute_name!r}')
    module = importlib.util.module_from_spec(spec)
    spec.loader.exec_module(module)
    sys.modules[absolute_name] = module
    if path is not None:
        setattr(parent_module, child_name, module)
    return module