importlib
--- import
的實作¶
在 3.1 版被加入.
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:
importlib.metadata
presents access to metadata from third-party distributions.importlib.resources
provides routines for accessing non-code "resources" from 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
insys.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 importpkg.mod
).The
import_module()
function acts as a simplifying wrapper aroundimportlib.__import__()
. This means all semantics of the function are derived fromimportlib.__import__()
. The most important difference between these two functions is thatimport_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 implementsinvalidate_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
..., callingreload()
for the other module does not redefine the objects imported from it --- one way around this is to re-execute thefrom
statement, another is to useimport
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 aModuleSpec
.
importlib.abc
-- Abstract base classes related to import¶
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 concreteMetaPathFinders
.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 onsys.meta_path
.在 3.4 版的變更: Returns
None
when called instead ofNotImplemented
.
- 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 byimportlib.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 concretePathEntryFinders
.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 byimportlib.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 intosys.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 fromsys.modules
; modules already insys.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):
module.__cached__
(已棄用)module.__package__
(已棄用)module.__loader__
(已棄用)
When
exec_module()
is available then backwards-compatible functionality is provided.在 3.4 版的變更: Raise
ImportError
when called instead ofNotImplementedError
. Functionality provided whenexec_module()
is available.在 3.4 版之後被棄用: The recommended API for loading a module is
exec_module()
(andcreate_module()
). Loaders should implement it instead ofload_module()
. The import machinery takes care of all the other responsibilities ofload_module()
whenexec_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 ofNotImplementedError
.
- 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 anImportError
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. ReturnsNone
if no source is available (e.g. a built-in module). RaisesImportError
if the loader cannot find the module specified.在 3.4 版的變更: Raises
ImportError
instead ofNotImplementedError
.
- 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 ofNotImplementedError
.
- 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 ofNotImplementedError
.
- class importlib.abc.FileLoader(fullname, path)¶
An abstract base class which inherits from
ResourceLoader
andExecutionLoader
, providing concrete implementations ofResourceLoader.get_data()
andExecutionLoader.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_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
andExecutionLoader
, requiring the implementation of:ExecutionLoader.get_filename()
Should only return the path to the source file; sourceless loading is not supported.
The abstract methods defined by this class are to add optional bytecode file support. Not implementing these optional methods (or causing them to raise
NotImplementedError
) causes the loader to only work with source code. Implementing the methods allows the loader to work with source and bytecode files; it does not allow for sourceless loading where only bytecode is provided. Bytecode files are an optimization to speed up loading by removing the parsing step of Python's compiler, and so no bytecode-specific API is exposed.- path_stats(path)¶
Optional abstract method which returns a
dict
containing metadata about the specified path. Supported dictionary keys are:'mtime'
(mandatory): an integer or floating-point number representing the modification time of the source code;'size'
(optional): the size in bytes of the source code.
Any other keys in the dictionary are ignored, to allow for future extensions. If the path cannot be handled,
OSError
is raised.在 3.3 版被加入.
在 3.4 版的變更: Raise
OSError
instead ofNotImplementedError
.
- 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. RaiseOSError
if the path cannot be handled.在 3.4 版的變更: Raise
OSError
instead ofNotImplementedError
.
- 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 byExecutionLoader.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 returnNone
. 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, will be removed in version 3.14: Use
importlib.resources.abc.TraversableResources
instead.- abstractmethod open_resource(resource)¶
Returns an opened, file-like object for binary reading of the resource.
If the resource cannot be found,
FileNotFoundError
is raised.
- abstractmethod resource_path(resource)¶
Returns the file system path to the resource.
If the resource does not concretely exist on the file system, raise
FileNotFoundError
.
- abstractmethod is_resource(name)¶
Returns
True
if the named name is considered a resource.FileNotFoundError
is raised if name does not exist.
- abstractmethod contents()¶
Returns an iterable of strings over the contents of the package. Do note that it is not required that all names returned by the iterator be actual resources, e.g. it is acceptable to return names for which
is_resource()
would be false.Allowing non-resource names to be returned is to allow for situations where how a package and its resources are stored are known a priori and the non-resource names would be useful. For instance, returning subdirectory names is allowed so that when it is known that the package and resources are stored on the file system then those subdirectory names can be used directly.
The abstract method returns an iterable of no items.
- class importlib.abc.Traversable¶
An object with a subset of
pathlib.Path
methods suitable for traversing directories and opening files.For a representation of the object on the file-system, use
importlib.resources.as_file()
.在 3.9 版被加入.
Deprecated since version 3.12, will be removed in version 3.14: Use
importlib.resources.abc.Traversable
instead.- name¶
Abstract. The base name of this object without any parent references.
- abstractmethod iterdir()¶
Yield
Traversable
objects inself
.
- abstractmethod is_dir()¶
Return
True
ifself
is a directory.
- abstractmethod is_file()¶
Return
True
ifself
is a file.
- abstractmethod joinpath(child)¶
Return Traversable child in
self
.
- abstractmethod __truediv__(child)¶
Return
Traversable
child inself
.
- 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. Subclassesimportlib.resources.abc.ResourceReader
and provides concrete implementations of theimportlib.resources.abc.ResourceReader
's abstract methods. Therefore, any loader supplyingimportlib.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, will be removed in version 3.14: Use
importlib.resources.abc.TraversableResources
instead.- abstractmethod files()¶
Returns a
importlib.resources.abc.Traversable
object for the loaded package.
importlib.machinery
-- Importers and path hooks¶
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 theimportlib.abc.MetaPathFinder
andimportlib.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()
andLoader.exec_module()
- class importlib.machinery.FrozenImporter¶
An importer for frozen modules. This class implements the
importlib.abc.MetaPathFinder
andimportlib.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()
andexec_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 theimportlib.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 insys.path_importer_cache
, thensys.path_hooks
is searched for a finder for the path entry and, if found, is stored insys.path_importer_cache
along with being queried about the module. If no finder is ever found thenNone
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 insys.path_importer_cache
.
- classmethod invalidate_caches()¶
Calls
importlib.abc.PathEntryFinder.invalidate_caches()
on all finders stored insys.path_importer_cache
that define the method. Otherwise entries insys.path_importer_cache
set toNone
are deleted.在 3.7 版的變更: Entries of
None
insys.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 ofFileFinder
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 subclassingimportlib.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.
- 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.
- 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.
- is_package(fullname)¶
Returns
True
if the file path points to a package's__init__
module based onEXTENSION_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.
- 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 toNone
.
- 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 beNone
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 asname
.
- 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 onsys.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 onsys.path
. The.fwork
file contains the path of the actual binary in theFrameworks
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 modulesources/foo/bar/_whiz.abi3.so
, withsources
being the location registered onsys.path
, relative to the application bundle. This module must be distributed asFrameworks/foo.bar._whiz.framework/foo.bar._whiz
(creating the framework name from the full import path of the module), with anInfo.plist
file in the.framework
directory identifying the binary as a framework. Thefoo.bar._whiz
module would be represented in the original location with asources/foo/bar/_whiz.abi3.fwork
marker file, containing the pathFrameworks/foo.bar._whiz/foo.bar._whiz
. The framework would also containFrameworks/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 traveral. 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 thePYTHONPATH
into frameworks in theFrameworks
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¶
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. Thecpython-32
string comes from the current magic tag (seeget_tag()
; ifsys.implementation.cache_tag
is not defined thenNotImplementedError
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 of2
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, elseValueError
is raised.The debug_override parameter is deprecated and can be used to override the system's value for
__debug__
. ATrue
value is the equivalent of setting optimization to the empty string. AFalse
value is the same as setting optimization to1
. If both debug_override an optimization are notNone
thenTypeError
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, aValueError
is raised. Ifsys.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 thespam
package).在 3.3 版被加入.
在 3.9 版的變更: To improve consistency with import statements, raise
ImportError
instead ofValueError
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
, thensys.modules[name].__spec__
is returned (unless the spec would beNone
or is not set, in which caseValueError
is raised). Otherwise a search usingsys.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 ofAttributeError
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 returnNone
, then any pre-existing attributes will not be reset. Also, noAttributeError
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 asInspectLoader.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 thesource_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'screate_module()
method must returnNone
or a type for which its__class__
attribute can be mutated along with not using slots. Finally, modules which substitute the object placed intosys.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 forimportlib.machinery.BuiltinImporter
andimportlib.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