importlib — The implementation of import — Python 3.8.20 documentation (original) (raw)

New in version 3.1.

Source code: Lib/importlib/__init__.py

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.

Functions¶

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

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

Note

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 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.

Changed in version 3.3: 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 caseValueError is raised). Otherwise a search using sys.meta_pathis done. 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.

New in version 3.3.

Changed in version 3.4: If __loader__ is not set, raise ValueError, just like when the attribute is set to None.

Deprecated since version 3.4: Use importlib.util.find_spec() instead.

importlib. invalidate_caches()¶

Invalidate the internal caches of finders stored atsys.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.

New in version 3.3.

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 trystatement 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 importand 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.

New in version 3.4.

Changed in version 3.7: ModuleNotFoundError is raised when the module being reloaded lacks a ModuleSpec.

Source code: Lib/importlib/abc.py

The importlib.abc module contains all of the core abstract base classes used by import. Some subclasses of the core abstract base classes are also provided to help in implementing the core ABCs.

ABC hierarchy:

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

class importlib.abc. Finder¶

An abstract base class representing a finder.

Deprecated since version 3.3: Use MetaPathFinder or PathEntryFinder instead.

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.

Changed in version 3.4: Returns None when called instead of raisingNotImplementedError.

class importlib.abc. MetaPathFinder¶

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

New in version 3.3.

find_spec(fullname, path, target=None)¶

An abstract method for finding a spec for the specified module. If this is a top-level import, path will be None. Otherwise, this is a search for a subpackage or module and path will be the value of __path__ from the parent package. If a spec cannot be found, None is returned. When passed in, target is a module object that the finder may use to make a more educated guess about what spec to return.importlib.util.spec_from_loader() may be useful for implementing concrete MetaPathFinders.

New in version 3.4.

find_module(fullname, path)¶

A legacy method for finding a loader 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 loader cannot be found, None is returned.

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

Changed in version 3.4: Returns None when called instead of raisingNotImplementedError. Can use find_spec() to provide functionality.

Deprecated since version 3.4: Use find_spec() instead.

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.

Changed in version 3.4: Returns None when called instead of NotImplemented.

class importlib.abc. PathEntryFinder¶

An abstract base class representing a path entry finder. Though it bears some similarities to MetaPathFinder, PathEntryFinderis meant for use only within the path-based import subsystem provided by PathFinder. This ABC is a subclass of Finder for compatibility reasons only.

New in version 3.3.

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, targetis 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.

New in version 3.4.

find_loader(fullname)¶

A legacy method for finding a loader for the specified module. Returns a 2-tuple of (loader, portion) where portionis 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 andportion is the empty list then no loader or location for a namespace package were found (i.e. failure to find anything for the module).

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

Changed in version 3.4: Returns (None, []) instead of raising NotImplementedError. Uses find_spec() when available to provide functionality.

Deprecated since version 3.4: Use find_spec() instead.

find_module(fullname)¶

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

Deprecated since version 3.4: Use find_spec() instead.

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. See PEP 302 for the exact definition for a loader.

Loaders that wish to support resource reading should implement aget_resource_reader(fullname) method as specified byimportlib.abc.ResourceReader.

Changed in version 3.7: 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.

New in version 3.4.

Changed in version 3.5: Starting in Python 3.6, this method will not be optional whenexec_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.

New in version 3.4.

Changed in version 3.6: 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 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 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 fully-qualified name of the package under which the module was loaded as a submodule (or the empty string for top-level modules). For packages, it is the same as __name__. Theimportlib.util.module_for_loader() decorator can handle the details for __package__.
__loader__
The loader used to load the module. Theimportlib.util.module_for_loader() decorator can handle the details for __package__.

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

Changed in version 3.4: Raise ImportError when called instead ofNotImplementedError. Functionality provided whenexec_module() is available.

Deprecated since version 3.4: 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(module)¶

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.

New in version 3.3.

Changed in version 3.4: Made optional instead of an abstractmethod.

Deprecated since version 3.4: The import machinery now takes care of this automatically.

class importlib.abc. ResourceReader¶

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__.pyfile 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 in a e.g. 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.

New in version 3.7.

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. ResourceLoader¶

An abstract base class for a loader which implements the optionalPEP 302 protocol for loading arbitrary resources from the storage back-end.

Deprecated since version 3.7: This ABC is deprecated in favour of supporting resource loading through importlib.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__.

class importlib.abc. InspectLoader¶

An abstract base class for a loader which implements the optionalPEP 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.

Note

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

Changed in version 3.4: No longer abstract and a concrete implementation is provided.

abstractmethod get_source(fullname)¶

An abstract method to return the source of a module. It is returned as a text string using universal newlines, translating all recognized line separators into '\n' characters. Returns Noneif no source is available (e.g. a built-in module). RaisesImportError if the loader cannot find the module specified.

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 theloader cannot find the module.

static source_to_code(data, path='')¶

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__).

New in version 3.4.

Changed in version 3.5: Made the method static.

exec_module(module)¶

Implementation of Loader.exec_module().

New in version 3.4.

load_module(fullname)¶

Implementation of Loader.load_module().

Deprecated since version 3.4: use exec_module() instead.

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.

class importlib.abc. FileLoader(fullname, path)¶

An abstract base class which inherits from ResourceLoader andExecutionLoader, providing concrete implementations ofResourceLoader.get_data() and ExecutionLoader.get_filename().

The fullname argument is a fully resolved name of the module the loader is to handle. The path argument is the path to the file for the module.

New in version 3.3.

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().

Deprecated since version 3.4: Use Loader.exec_module() instead.

abstractmethod get_filename(fullname)¶

Returns path.

abstractmethod get_data(path)¶

Reads path as a binary file and returns the bytes from it.

class importlib.abc. SourceLoader¶

An abstract base class for implementing source (and optionally bytecode) file loading. The class inherits from both ResourceLoader andExecutionLoader, 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 is raised.

New in version 3.3.

path_mtime(path)¶

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

Deprecated since version 3.3: 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.

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.

get_code(fullname)¶

Concrete implementation of InspectLoader.get_code().

exec_module(module)¶

Concrete implementation of Loader.exec_module().

New in version 3.4.

load_module(fullname)¶

Concrete implementation of Loader.load_module().

Deprecated since version 3.4: 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__.

importlib.resources – Resources¶

Source code: Lib/importlib/resources.py

New in version 3.7.

This module leverages Python’s import system to provide access to _resources_within packages. If you can import a package, you can access resources within that package. Resources can be opened or read, in either binary or text mode.

Resources are roughly akin to files inside directories, though it’s important to keep in mind that this is just a metaphor. Resources and packages do not have to exist as physical files and directories on the file system.

Loaders that wish to support resource reading should implement aget_resource_reader(fullname) method as specified byimportlib.abc.ResourceReader.

The following types are defined.

importlib.resources. Package¶

The Package type is defined as Union[str, ModuleType]. This means that where the function describes accepting a Package, you can pass in either a string or a module. Module objects must have a resolvable__spec__.submodule_search_locations that is not None.

importlib.resources. Resource¶

This type describes the resource names passed into the various functions in this package. This is defined as Union[str, os.PathLike].

The following functions are available.

importlib.resources. open_binary(package, resource)¶

Open for binary reading the resource within package.

package is either a name or a module object which conforms to thePackage requirements. resource is the name of the resource to open within package; it may not contain path separators and it may not have sub-resources (i.e. it cannot be a directory). This function returns atyping.BinaryIO instance, a binary I/O stream open for reading.

importlib.resources. open_text(package, resource, encoding='utf-8', errors='strict')¶

Open for text reading the resource within package. By default, the resource is opened for reading as UTF-8.

package is either a name or a module object which conforms to thePackage requirements. resource is the name of the resource to open within package; it may not contain path separators and it may not have sub-resources (i.e. it cannot be a directory). encoding and _errors_have the same meaning as with built-in open().

This function returns a typing.TextIO instance, a text I/O stream open for reading.

importlib.resources. read_binary(package, resource)¶

Read and return the contents of the resource within package asbytes.

importlib.resources. read_text(package, resource, encoding='utf-8', errors='strict')¶

Read and return the contents of resource within package as a str. By default, the contents are read as strict UTF-8.

package is either a name or a module object which conforms to thePackage requirements. resource is the name of the resource to open within package; it may not contain path separators and it may not have sub-resources (i.e. it cannot be a directory). encoding and _errors_have the same meaning as with built-in open(). This function returns the contents of the resource as str.

importlib.resources. path(package, resource)¶

Return the path to the resource as an actual file system path. This function returns a context manager for use in a with statement. The context manager provides a pathlib.Path object.

Exiting the context manager cleans up any temporary file created when the resource needs to be extracted from e.g. a zip file.

importlib.resources. is_resource(package, name)¶

Return True if there is a resource named name in the package, otherwise False. Remember that directories are not resources!package is either a name or a module object which conforms to thePackage requirements.

importlib.resources. contents(package)¶

Return an iterable over the named items within the package. The iterable returns str resources (e.g. files) and non-resources (e.g. directories). The iterable does not recurse into subdirectories.

package is either a name or a module object which conforms to thePackage requirements.

importlib.machinery – Importers and path hooks¶

Source code: Lib/importlib/machinery.py

This module contains the various objects that help importfind and load modules.

importlib.machinery. SOURCE_SUFFIXES¶

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

New in version 3.3.

importlib.machinery. DEBUG_BYTECODE_SUFFIXES¶

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

New in version 3.3.

Deprecated since version 3.5: Use BYTECODE_SUFFIXES instead.

importlib.machinery. OPTIMIZED_BYTECODE_SUFFIXES¶

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

New in version 3.3.

Deprecated since version 3.5: Use BYTECODE_SUFFIXES instead.

importlib.machinery. BYTECODE_SUFFIXES¶

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

New in version 3.3.

Changed in version 3.5: The value is no longer dependent on __debug__.

importlib.machinery. EXTENSION_SUFFIXES¶

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

New in version 3.3.

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()).

New in version 3.3.

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.

Changed in version 3.5: As part of PEP 489, the builtin importer now implementsLoader.create_module() and Loader.exec_module()

class importlib.machinery. FrozenImporter¶

An importer for frozen modules. This class implements theimportlib.abc.MetaPathFinder andimportlib.abc.InspectLoader ABCs.

Only class methods are defined by this class to alleviate the need for instantiation.

Changed in version 3.4: Gained create_module() and exec_module()methods.

class importlib.machinery. WindowsRegistryFinder¶

Finder for modules declared in the Windows registry. This class implements the importlib.abc.MetaPathFinder ABC.

Only class methods are defined by this class to alleviate the need for instantiation.

New in version 3.3.

Deprecated since version 3.6: Use site configuration instead. Future versions of Python may not enable this finder by default.

class importlib.machinery. PathFinder¶

A Finder for sys.path and package __path__ attributes. This class implements the importlib.abc.MetaPathFinder ABC.

Only class methods are defined by this class to alleviate the need for instantiation.

classmethod find_spec(fullname, path=None, target=None)¶

Class method that attempts to find a specfor 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, 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.

New in version 3.4.

Changed in version 3.5: 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().

Deprecated since version 3.4: Use find_spec() instead.

classmethod invalidate_caches()¶

Calls importlib.abc.PathEntryFinder.invalidate_caches() on all finders stored in sys.path_importer_cache that define the method. Otherwise entries in sys.path_importer_cache set to None are deleted.

Changed in version 3.4: 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().

New in version 3.3.

path¶

The path the finder will search in.

find_spec(fullname, target=None)¶

Attempt to find the spec to handle fullname within path.

New in version 3.4.

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 is raised.

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

A concrete implementation of importlib.abc.SourceLoader by subclassing importlib.abc.FileLoader and providing some concrete implementations of other methods.

New in version 3.3.

name¶

The name of the module that this loader will handle.

path¶

The path to the source file.

is_package(fullname)¶

Return True if path appears to be for a package.

path_stats(path)¶

Concrete implementation of importlib.abc.SourceLoader.path_stats().

set_data(path, data)¶

Concrete implementation of importlib.abc.SourceLoader.set_data().

load_module(name=None)¶

Concrete implementation of importlib.abc.Loader.load_module() where specifying the name of the module to load is optional.

Deprecated since version 3.6: 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.

New in version 3.3.

name¶

The name of the module the loader will handle.

path¶

The path to the bytecode file.

is_package(fullname)¶

Determines if the module is a package based on path.

get_code(fullname)¶

Returns the code object for name created from path.

get_source(fullname)¶

Returns None as bytecode files have no source when this loader is used.

load_module(name=None)¶

Concrete implementation of importlib.abc.Loader.load_module() where specifying the name of the module to load is optional.

Deprecated since version 3.6: 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.

New in version 3.3.

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.

New in version 3.5.

exec_module(module)¶

Initializes the given module object in accordance with PEP 489.

New in version 3.5.

is_package(fullname)¶

Returns True if the file path points to a package’s __init__module based on EXTENSION_SUFFIXES.

get_code(fullname)¶

Returns None as extension modules lack a code object.

get_source(fullname)¶

Returns None as extension modules do not have source code.

get_filename(fullname)¶

Returns path.

New in version 3.4.

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.

New in version 3.4.

name¶

(__name__)

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

loader¶

(__loader__)

The Loader that should be used when loading the module. Finders should always set this.

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 (e.g. for namespace packages).

submodule_search_locations¶

(__path__)

List of strings for where to find submodules, if a package (Noneotherwise).

loader_state¶

Container of extra module-specific data for use during loading (orNone).

cached¶

(__cached__)

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

parent¶

(__package__)

(Read-only) The fully-qualified name of the package under which the module should be loaded as a submodule (or the empty string for top-level modules). For packages, it is the same as __name__.

has_location¶

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

importlib.util – Utility code for importers¶

Source code: 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.

New in version 3.4.

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

Return the PEP 3147/PEP 488 path to the byte-compiled file associated with the source path. For example, if path is /foo/bar/baz.py the return value would be /foo/bar/__pycache__/baz.cpython-32.pyc for Python 3.2. The cpython-32 string comes from the current magic tag (seeget_tag(); if sys.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, else ValueError is raised.

The debug_override parameter is deprecated and can be used to override the system’s value for __debug__. A True value is the equivalent of setting optimization to the empty string. A False value is the same as setting optimization to 1. If both debug_override an _optimization_are not None then TypeError is raised.

New in version 3.4.

Changed in version 3.5: The optimization parameter was added and the debug_override parameter was deprecated.

importlib.util. source_from_cache(path)¶

Given the path to a PEP 3147 file name, return the associated source code file path. For example, if path is/foo/bar/__pycache__/baz.cpython-32.pyc the returned path would be/foo/bar/baz.py. path need not exist, however if it does not conform to PEP 3147 or PEP 488 format, a ValueError is raised. Ifsys.implementation.cache_tag is not defined,NotImplementedError is raised.

New in version 3.4.

importlib.util. decode_source(source_bytes)¶

Decode the given bytes representing source code and return it as a string with universal newlines (as required byimportlib.abc.InspectLoader.get_source()).

New in version 3.4.

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 asimportlib.util.resolve_name('sys', __spec__.parent) 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).

New in version 3.3.

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 beNone or is not set, in which case ValueError is raised). Otherwise a search using sys.meta_path is done. None is returned if no spec is found.

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

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

New in version 3.4.

importlib.util. module_from_spec(spec)¶

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

If spec.loader.create_moduledoes not return None, then any pre-existing attributes will not be reset. Also, no AttributeError will be raised if triggered while accessingspec 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.

New in version 3.5.

@ importlib.util. module_for_loader¶

A decorator 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 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 insys.modules then a new one is constructed. Regardless of where the module came from, __loader__ set to 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 tosys.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.

Changed in version 3.3: __loader__ and __package__ are automatically set (when possible).

Deprecated since version 3.4: The import machinery now directly performs all the functionality provided by this function.

@ importlib.util. set_loader¶

A decorator 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.

Changed in version 3.4: Set __loader__ if set to None, as if the attribute does not exist.

Deprecated since version 3.4: The import machinery takes care of this automatically.

@ importlib.util. set_package¶

A decorator 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.

Deprecated since version 3.4: 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 asInspectLoader.is_package(), to fill in any missing information on the spec.

New in version 3.4.

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.

New in version 3.4.

importlib.util. source_hash(source_bytes)¶

Return the hash of source_bytes as bytes. A hash-based .pyc file embeds the source_hash() of the corresponding source file’s contents in its header.

New in version 3.7.

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 defineexec_module() as control over what module type is used for the module is required. For those same reasons, the loader’screate_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.

Note

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 isheavily discouraged due to error messages created during loading being postponed and thus occurring out of context.

New in version 3.5.

Changed in version 3.6: Began calling create_module(), removing the compatibility warning for importlib.machinery.BuiltinImporter andimportlib.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))

Examples¶

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().

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¶

To import a Python source file directly, use the following recipe (Python 3.5 and newer only):

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)

Setting up an importer¶

For deep customizations of import, you typically want to implement animporter. This means managing both the finder and loaderside 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 ofimportlib.import_module() (Python 3.4 and newer for the importlib usage, Python 3.6 and newer for other parts of the code).

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

importlib — The implementation of import — Python 3.8.20 documentation (original) (raw)

Introduction¶

Functions¶

importlib.abc – Abstract base classes related to import¶

importlib.resources – Resources¶

importlib.machinery – Importers and path hooks¶

importlib.util – Utility code for importers¶

Examples¶

Importing programmatically¶

Checking if a module can be imported¶

For illustrative purposes.

Importing a source file directly¶

For illustrative purposes.

Setting up an importer¶

For illustrative purposes only.

Setting up a meta path finder.

Make sure to put the finder in the proper location in the list in terms of

priority.

Setting up a path entry finder.

Make sure to put the path hook in the proper location in the list in terms

of priority.

Approximating importlib.import_module()¶