importlib
— 实现为
import
¶
3.1 版新增。
源代码： Lib/importlib/__init__.py
目地对于
importlib
package is three-fold.
One is to provide the implementation of the
import
statement (and thus, by extension, the
__import__()
function) in Python source code. This provides an implementation of
import
which is portable to any Python interpreter. This also provides an implementation which is easier to comprehend than one implemented in a programming language other than Python.
Two, the components to implement
import
are exposed in this package, making it easier for users to create their own custom objects (known generically as an
importer
) to participate in the import process.
Three, the package contains modules exposing additional functionality for managing aspects of Python packages:
importlib.metadata
presents access to metadata from third-party distributions.
importlib.resources
provides routines for accessing non-code “resources” from Python packages.
另请参阅
The language reference for the
import
语句。
Original specification of packages. Some semantics have changed since the writing of this document (e.g. redirecting based on
None
in
sys.modules
).
__import__()
function
import
语句是用于此函数的句法糖。
The initialization of
sys.path
.
在不区分大小写的平台导入
定义 Python 源代码编码
新的导入挂钩
Imports: Multi-Line and Absolute/Relative
Main module explicit relative imports
隐式名称空间包
A ModuleSpec Type for the Import System
Elimination of PYO files
Multi-phase extension module initialization
Deterministic pycs
使用 UTF-8 作为默认源编码
PYC 存储库目录
实现内置
__import__()
函数。
注意
以编程方式导入模块应该使用
import_module()
而不是此函数。
导入模块。
name
自变量按绝对 (或相对) 术语方式指定要导入什么模块 (如
pkg.mod
or
..mod
)。若名称以相对术语方式指定，那么
package
自变量必须被设为充当解析包名的锚点包的名称 (如
import_module('..mod', 'pkg.subpkg')
将导入
pkg.mod
).
import_module()
函数充当简化包裹器围绕
importlib.__import__()
。这意味着函数的所有语义均派生自
importlib.__import__()
。这 2 函数的最重要区别是
import_module()
返回指定包或模块 (如
pkg.mod
)，而
__import__()
返回顶层包或模块 (如
pkg
).
若要动态导入从解释器开始执行起创建的模块 (如：创建 Python 源文件)，可能需要调用
invalidate_caches()
为使新模块能被导入系统注意到。
3.3 版改变： 自动导入父级包。
查找模块加载器，可选指定
path
。若模块在
sys.modules
，那么
sys.modules[name].__loader__
被返回 (除非加载器将为
None
或未设置，在这种情况下
ValueError
被引发)。否则，搜索使用
sys.meta_path
完成。
None
被返回，若找不到加载器。
带点名称不会隐式导入其父级，因为这将要求加载父级，而父级可能不期望这样。要正确导入子模块，需要导入子模块的所有父级包，并使用正确自变量 path .
3.3 版新增。
3.4 版改变：
若
__loader__
未设置，引发
ValueError
，就像当把属性设为
None
.
从 3.4 版起弃用：
使用
importlib.util.find_spec()
代替。
使内部缓存无效的查找器存储在
sys.meta_path
。若查找器有实现
invalidate_caches()
那么调用它将履行无效操作。应调用此函数，若运行程序时有创建/安装任何模块，以保证所有查找器都注意到新模块的存在。
3.3 版新增。
3.10 版改变：
Namespace packages created/installed in a different
sys.path
location after the same namespace was already imported are noticed.
重新加载先前导入的
module
。自变量是模块对象，所以之前必须成功导入它。这很有用，若有使用外部编辑器编辑模块源文件，且想要不离开 Python 解释器试用新版本。返回值是模块对象 (可能不同，若重新导入导致不同对象被放置在
sys.modules
).
当
reload()
被执行：
Python 模块代码被重新编译且模块级代码被重新执行，定义被绑定到模块字典名称的一组新对象通过重用
loader
最初加载模块。
init
函数对于扩展模块不会被 2 次调用。
如 Python 所有其它对象，旧对象仅在其引用计数降至 0 后才被回收。
更新模块名称空间中的名称，以指向任何新的 (或更改) 对象。
旧对象的其它引用 (譬如：模块外部名称) 不会重新绑定到新对象引用，且必须更新它们出现的每个名称空间，若期望。
有很多其它告诫：
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
) 代替。
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。
3.7 版改变：
ModuleNotFoundError
被引发，当重新加载模块缺少
ModuleSpec
.
importlib.abc
– 导入相关 ABC (抽象基类)
¶
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
An abstract base class representing a finder .
从 3.3 版起弃用：
使用
MetaPathFinder
or
PathEntryFinder
代替。
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
当调用而不是引发
NotImplementedError
.
从 3.10 版起弃用：
实现
MetaPathFinder.find_spec()
or
PathEntryFinder.find_spec()
代替。
An abstract base class representing a 元路径查找器 .
3.3 版新增。
3.10 版改变：
No longer a subclass of
Finder
.
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.
importlib.util.spec_from_loader()
may be useful for implementing concrete
MetaPathFinders
.
3.4 版新增。
传统方法用于查找
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
当调用而不是引发
NotImplementedError
。可以使用
find_spec()
来提供功能。
从 3.4 版起弃用：
使用
find_spec()
代替。
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
当调用而不是
NotImplemented
.
An abstract base class representing a
路径条目查找器
. Though it bears some similarities to
MetaPathFinder
,
PathEntryFinder
is meant for use only within the path-based import subsystem provided by
importlib.machinery.PathFinder
.
3.3 版新增。
3.10 版改变：
No longer a subclass of
Finder
.
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.
importlib.util.spec_from_loader()
may be useful for implementing concrete
PathEntryFinders
.
3.4 版新增。
传统方法用于查找
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, [])
而不是引发
NotImplementedError
. Uses
find_spec()
when available to provide functionality.
从 3.4 版起弃用：
使用
find_spec()
代替。
A concrete implementation of
Finder.find_module()
相当于
self.find_loader(fullname)[0]
.
从 3.4 版起弃用：
使用
find_spec()
代替。
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.
An abstract base class for a loader 。见 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
.
3.7 版改变：
Introduced the optional
get_resource_reader()
方法。
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。
3.6 版改变：
This method is no longer optional when
exec_module()
有定义。
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()
必须有定义。
3.4 版新增。
3.6 版改变：
create_module()
must also be defined.
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 module’s fully qualified name. It is
'__main__'
for an executed module.
__cached__
The filename of a compiled version of the module’s code. It is not set on all modules (e.g. built-in modules).
__path__
The list of locations where the package’s submodules will be found. Most of the time this is a single directory. The import system passes this attribute to
__import__()
and to finders in the same way as
sys.path
but just for the package. It is not set on non-package modules so it can be used as an indicator that the module is a package.
__package__
The fully qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as
__name__
.
__loader__
loader used to load the module.
当
exec_module()
is available then backwards-compatible functionality is provided.
3.4 版改变：
引发
ImportError
当调用而不是
NotImplementedError
. Functionality provided when
exec_module()
可用。
从 3.4 版起弃用：
The recommended API for loading a module is
exec_module()
(和
create_module()
). Loaders should implement it instead of
load_module()
. The import machinery takes care of all the other responsibilities of
load_module()
当
exec_module()
is implemented.
A legacy method which when implemented calculates and returns the given module’s representation, 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.
An abstract base class for a loader which implements the optional PEP 302 protocol for loading arbitrary resources from the storage back-end.
从 3.7 版起弃用：
This ABC is deprecated in favour of supporting resource loading through
importlib.resources.abc.ResourceReader
.
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
.
An abstract base class for a loader which implements the optional PEP 302 protocol for loaders that inspect modules.
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.
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
.
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.
3.4 版改变：
引发
ImportError
而不是
NotImplementedError
.
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.
Implementation of
Loader.exec_module()
.
3.4 版新增。
Implementation of
Loader.load_module()
.
从 3.4 版起弃用：
使用
exec_module()
代替。
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。
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
.
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。
The name of the module the loader can handle.
模块文件的路径。
Calls super’s
load_module()
.
从 3.4 版起弃用：
使用
Loader.exec_module()
代替。
读取 path as a binary file and returns the bytes from it.
An abstract base class for implementing source (and optionally bytecode) file loading. The class inherits from both
ResourceLoader
and
ExecutionLoader
, 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.
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
.
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
.
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
)，不传播异常。
3.4 版改变：
不再引发
NotImplementedError
当调用时。
具体实现的
InspectLoader.get_code()
.
具体实现的
Loader.exec_module()
.
3.4 版新增。
具体实现的
Loader.load_module()
.
从 3.4 版起弃用：
使用
exec_module()
代替。
具体实现的
InspectLoader.get_source()
.
具体实现的
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
– 导入器和路径挂钩
¶
源代码： Lib/importlib/machinery.py
此模块包含的各种对象帮助
import
查找和加载模块。
A list of strings representing the recognized file suffixes for source modules.
3.3 版新增。
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。
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。
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：
值不再从属
__debug__
.
A list of strings representing the recognized file suffixes for extension modules.
3.3 版新增。
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。
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()
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.
3.4 版改变：
Gained
create_module()
and
exec_module()
方法。
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.
A
Finder
for
sys.path
和包
__path__
attributes. This class implements the
importlib.abc.MetaPathFinder
ABC.
Only class methods are defined by this class to alleviate the need for instantiation.
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
路径条目查找器
to look for the module being searched for. If no entry is found in
sys.path_importer_cache
，那么
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
.
A legacy wrapper around
find_spec()
.
从 3.4 版起弃用：
使用
find_spec()
代替。
调用
importlib.abc.PathEntryFinder.invalidate_caches()
on all finders stored in
sys.path_importer_cache
that define the method. Otherwise entries in
sys.path_importer_cache
设为
None
被删除。
3.7 版改变：
Entries of
None
in
sys.path_importer_cache
被删除。
3.4 版改变：
Calls objects in
sys.path_hooks
with the current working directory for
''
(i.e. the empty string).
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。
The path the finder will search in.
Attempt to find the spec to handle
fullname
在
path
.
3.4 版新增。
Attempt to find the loader to handle
fullname
在
path
.
从 3.10 版起弃用：
使用
find_spec()
代替。
Clear out the internal cache.
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。
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。
The name of the module that this loader will handle.
源文件路径。
具体实现的
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。
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。
The name of the module the loader will handle.
The path to the bytecode file.
返回
None
as bytecode files have no source when this loader is used.
具体实现的
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。
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 of the module the loader supports.
Path to the extension module.
Creates the module object from the given specification in accordance with PEP 489 .
3.5 版新增。
返回
True
if the file path points to a package’s
__init__
module based on
EXTENSION_SUFFIXES
.
返回
None
as extension modules lack a code object.
返回
None
as extension modules do not have source code.
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
3.11 版新增。
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
值
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.
3.4 版新增。
(
__name__
)
The module’s fully qualified name. The finder should always set this attribute to a non-empty string.
(
__loader__
)
loader used to load the module. The finder should always set this attribute.
(
__file__
)
The location the
loader
should use to load the module. For example, for modules loaded from a .py file this is the filename. The
finder
should always set this attribute to a meaningful value for the
loader
to use. In the uncommon case that there is not one (like for namespace packages), it should be set to
None
.
(
__path__
)
The list of locations where the package’s submodules will be found. Most of the time this is a single directory. The
finder
should set this attribute to a list, even an empty one, to indicate to the import system that the module is a package. It should be set to
None
for non-package modules. It is set automatically later to a special object for namespace packages.
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. The
finder
should always set this attribute but it may be
None
for modules that do not need compiled code stored.
(
__package__
)
(Read-only) The fully qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as
name
.
True
if the spec’s
origin
refers to a loadable location,
False
otherwise. This value impacts how
origin
is interpreted and how the module’s
__file__
is populated.
importlib.util
– 用于导入器的实用程序代码
¶
This module contains the various objects that help in the construction of an importer .
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。
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. The
cpython-32
string comes from the current magic tag (see
get_tag()
；若
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 interpreter’s optimization level to be used. Any other value’s string representation is used, so
/foo/bar/baz.py
with an
optimization
of
2
will lead to the bytecode path of
/foo/bar/__pycache__/baz.cpython-32.opt-2.pyc
. The string representation of
optimization
can only be alphanumeric, else
ValueError
被引发。
debug_override
parameter is deprecated and can be used to override the system’s value for
__debug__
。
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 .
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
被引发。若
sys.implementation.cache_tag
未定义，
NotImplementedError
被引发。
3.4 版新增。
3.6 版改变： 接受 像路径对象 .
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。
Resolve a relative module name to an absolute one.
若
名称
has no leading dots, then
名称
is simply returned. This allows for usage such as
importlib.util.resolve_name('sys', __spec__.parent)
without doing a check to see if the
包
argument is needed.
ImportError
被引发若
名称
is a relative module name but
包
is a false value (e.g.
None
or the empty string).
ImportError
is also raised if a relative name would escape its containing package (e.g. requesting
..bacon
from within the
spam
package).
3.3 版新增。
3.9 版改变：
To improve consistency with import statements, raise
ImportError
而不是
ValueError
for invalid relative import attempts.
Find the
spec
for a module, optionally relative to the specified
包
name. If the module is in
sys.modules
，那么
sys.modules[name].__spec__
is returned (unless the spec would be
None
或未设置，在这种情况下
ValueError
被引发)。否则，搜索使用
sys.meta_path
完成。
None
is returned if no spec is found.
若 名称 is for a submodule (contains a dot), the parent module is automatically imported.
名称
and
包
work the same as for
import_module()
.
3.4 版新增。
3.7 版改变：
引发
ModuleNotFoundError
而不是
AttributeError
if
包
is in fact not a package (i.e. lacks a
__path__
属性)。
Create a new module based on
spec
and
spec.loader.create_module
.
若
spec.loader.create_module
不返回
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。
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, module)
) for which the second argument will be the module
对象
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
名称
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.
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.
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.
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。
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 .
Return the hash of
source_bytes
as bytes. A hash-based
.pyc
file embeds the
source_hash()
of the corresponding source file’s contents in its header.
3.7 版新增。
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
.
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))
To programmatically import a module, use
importlib.import_module()
.
import importlib itertools = importlib.import_module('itertools')
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()
.
注意，若
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")
To import a Python source file directly, use the following recipe:
import importlib.util import sys # For illustrative purposes. import tokenize file_path = tokenize.__file__ module_name = tokenize.__name__ spec = importlib.util.spec_from_file_location(module_name, file_path) module = importlib.util.module_from_spec(spec) sys.modules[module_name] = module spec.loader.exec_module(module)
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
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
元路径查找器
或
路径条目查找器
. The former is what you would put on
sys.meta_path
while the latter is what you create using a
路径条目挂钩
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))
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