importlib — The implementation of import — Python documentation
importlib — The implementation of import
New in version 3.1.
Source code: :source:`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.
See also
- The import statement
- The language reference for the import statement.
- Packages specification
- Original specification of packages. Some semantics have changed since the writing of this document (e.g. redirecting based on
None
in sys.modules). - The __import__() function
- The import statement is syntactic sugar for this function.
- 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
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 around importlib.__import__(). This means all semantics of the function are derived from importlib.__import__(). The most important difference between these two functions is that import_module() returns the specified package or module (e.g.
pkg.mod
), while __import__() returns the top-level package or module (e.g.pkg
).If you are dynamically importing a module that was created since the interpreter began execution (e.g., created a Python source file), you may need to call invalidate_caches() in order for the new module to be noticed by the import system.
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 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 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 toNone
.Deprecated since version 3.4: Use importlib.util.find_spec() instead.
- importlib.invalidate_caches()
Invalidate the internal caches of finders stored at sys.meta_path. If a finder implements
invalidate_caches()
then it will be called to perform the invalidation. This function should be called if any modules are created/installed while your program is running to guarantee all finders will notice the new module’s existence.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 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 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.
New in version 3.4.
Changed in version 3.7: ModuleNotFoundError is raised when the module being reloaded lacks a
ModuleSpec
.
Source code: :source:`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.
- 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 concreteMetaPathFinders
.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 raising NotImplementedError. 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 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 byPathFinder
. 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,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
.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)
whereportion
is a sequence of file system locations contributing to part of a namespace package. The loader may beNone
while specifyingportion
to signify the contribution of the file system locations to a namespace package. An empty list can be used forportion
to signify the loader is not part of a namespace package. Ifloader
isNone
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 toself.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 a
get_resource_reader(fullname)
method as specified by importlib.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 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.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 into sys.modules before any loading begins, to prevent recursion from the import. If the loader inserted a module and the load fails, it must be removed by the loader from sys.modules; modules already in sys.modules before the loader began execution should be left alone (see importlib.util.module_for_loader()).
The loader should set several attributes on the module. (Note that some of these attributes can change when a module is reloaded):
__name__
The name of the module.
__file__
The path to where the module data is stored (not set for built-in modules).
__cached__
The path to where a compiled version of the module is/should be stored (not set when the attribute would be inappropriate).
__path__
A list of strings specifying the search path within a package. This attribute is not set on modules.
__package__
The 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__. The importlib.util.module_for_loader() decorator can handle the details for __package__.
__loader__
The loader used to load the module. The importlib.util.module_for_loader() decorator can handle the details for __package__.
When exec_module() is available then backwards-compatible functionality is provided.
Changed in version 3.4: Raise ImportError when called instead of NotImplementedError. Functionality provided when exec_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
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 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 return None. An object compatible with this ABC should only be returned when the specified module is a package.New in version 3.7.
- 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.
Deprecated since version 3.7: This ABC is deprecated in favour of supporting resource loading through importlib.abc.ResourceReader.
- class importlib.abc.InspectLoader
An abstract base class for a loader which implements the optional PEP 302 protocol for loaders that inspect modules.
- get_code(fullname)
Return the code object for a module, or
None
if the module does not have a code object (as would be the case, for example, for a built-in module). Raise an ImportError if loader cannot find the requested module.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.
- 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.
Changed in version 3.4: Raises ImportError instead of NotImplementedError.
- static source_to_code(data, path='<string>')
Create a code object from Python source.
The data argument can be whatever the compile() function supports (i.e. string or bytes). The path argument should be the “path” to where the source code originated from, which can be an abstract concept (e.g. location in a zip file).
With the subsequent code object one can execute it in a module by running
exec(code, module.__dict__)
.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.
- class importlib.abc.FileLoader(fullname, path)
An abstract base class which inherits from ResourceLoader and ExecutionLoader, providing concrete implementations of
ResourceLoader.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.
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.
- class importlib.abc.SourceLoader
An abstract base class for implementing source (and optionally bytecode) file loading. The class inherits from both ResourceLoader and ExecutionLoader, requiring the implementation of:
ResourceLoader.get_data()
ExecutionLoader.get_filename()
Should only return the path to the source file; sourceless loading is not supported.
The abstract methods defined by this class are to add optional bytecode file support. Not implementing these optional methods (or causing them to raise NotImplementedError) causes the loader to only work with source code. Implementing the methods allows the loader to work with source and bytecode files; it does not allow for sourceless loading where only bytecode is provided. Bytecode files are an optimization to speed up loading by removing the parsing step of Python’s compiler, and so no bytecode-specific API is exposed.
- path_stats(path)
Optional abstract method which returns a dict containing metadata about the specified path. Supported dictionary keys are:
'mtime'
(mandatory): an integer or floating-point number representing the modification time of the source code;'size'
(optional): the size in bytes of the source code.
Any other keys in the dictionary are ignored, to allow for future extensions. If the path cannot be handled, OSError is raised.
New in version 3.3.
Changed in version 3.4: Raise OSError instead of NotImplementedError.
- 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.
Changed in version 3.4: Raise OSError instead of NotImplementedError.
- set_data(path, data)
Optional abstract method which writes the specified bytes to a file path. Any intermediate directories which do not exist are to be created automatically.
When writing to the path fails because the path is read-only (errno.EACCES/PermissionError), do not propagate the exception.
Changed in version 3.4: No longer raises NotImplementedError when called.
- 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 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__
.
- class importlib.abc.Traversable
An object with a subset of pathlib.Path methods suitable for traversing directories and opening files.
New in version 3.9.
- 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
files
interface. Subclasses ResourceReader and provides concrete implementations of the ResourceReader’s abstract methods. Therefore, any loader supplying TraversableReader also supplies ResourceReader.New in version 3.9.
importlib.resources – Resources
Source code: :source:`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.
Note
This module provides functionality similar to pkg_resources Basic Resource Access without the performance overhead of that package. This makes reading resources included in packages easier, with more stable and consistent semantics.
The standalone backport of this module provides more information on using importlib.resources and migrating from pkg_resources to importlib.resources.
Loaders that wish to support resource reading should implement a get_resource_reader(fullname)
method as specified by importlib.abc.ResourceReader.
The following types are defined.
- importlib.resources.Package
- The
Package
type is defined asUnion[str, ModuleType]
. This means that where the function describes accepting aPackage
, you can pass in either a string or a module. Module objects must have a resolvable__spec__.submodule_search_locations
that is notNone
.
- 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.files(package)
Returns an
importlib.resources.abc.Traversable
object representing the resource container for the package (think directory) and its resources (think files). A Traversable may contain other containers (think subdirectories).package is either a name or a module object which conforms to the
Package
requirements.New in version 3.9.
- importlib.resources.as_file(traversable)
Given a
importlib.resources.abc.Traversable
object representing a file, typically from importlib.resources.files(), return 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 was extracted from e.g. a zip file.
Use
as_file
when the Traversable methods (read_text
, etc) are insufficient and an actual file on the file system is required.New in version 3.9.
- 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 the
Package
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 the
Package
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 as
bytes
.package is either a name or a module object which conforms to the
Package
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 the contents of the resource as bytes.
- 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 the
Package
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.
package is either a name or a module object which conforms to the
Package
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).
- importlib.resources.is_resource(package, name)
- Return
True
if there is a resource named name in the package, otherwiseFalse
. 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 the
Package
requirements.
importlib.machinery – Importers and path hooks
Source code: :source:`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.
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 the importlib.abc.MetaPathFinder and importlib.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 implements
Loader.create_module()
andLoader.exec_module()
- class importlib.machinery.FrozenImporter
An importer for frozen modules. This class implements the importlib.abc.MetaPathFinder and importlib.abc.InspectLoader ABCs.
Only class methods are defined by this class to alleviate the need for instantiation.
Changed in version 3.4: 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.
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 spec for the module specified by fullname on sys.path or, if defined, on path. For each path entry that is searched, sys.path_importer_cache is checked. If a non-false object is found then it is used as the path entry finder to look for the module being searched for. If no entry is found in sys.path_importer_cache, then sys.path_hooks is searched for a finder for the path entry and, if found, is stored in sys.path_importer_cache along with being queried about the module. If no finder is ever found then
None
is both stored in the cache and returned.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 3.7: Entries of
None
in sys.path_importer_cache 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_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 (
None
otherwise).- loader_state
Container of extra module-specific data for use during loading (or
None
).- cached
(
__cached__
)String for where the compiled module should be stored (or
None
).- parent
(
__package__
)(Read-only) 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: :source:`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. Thecpython-32
string comes from the current magic tag (seeget_tag()
; ifsys.implementation.cache_tag
is not defined then NotImplementedError 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 ofwill 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__
. 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
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.
Changed in version 3.6: 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, a ValueError is raised. Ifsys.implementation.cache_tag
is not defined, NotImplementedError is raised.New in version 3.4.
Changed in version 3.6: 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()
).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 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 a relative name would escape its containing package (e.g. requesting..bacon
from within thespam
package).New in version 3.3.
Changed in version 3.9: To improve consistency with import statements, raise ImportError instead of ValueError 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, 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.
Changed in version 3.7: Raises ModuleNotFoundError instead of AttributeError 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 return
None
, then any pre-existing attributes will not be reset. Also, no AttributeError will be raised if triggered while accessing spec or setting an attribute on the module.This function is preferred over using types.ModuleType to create a new module as spec is used to set as many import-controlled attributes on the module as possible.
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 in sys.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 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.
Changed in version 3.3: __loader__ and __package__ are automatically set (when possible).
Changed in version 3.4: Set __name__, __loader__ __package__ unconditionally to support reloading.
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 toNone
, 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.
Changed in version 3.6: 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 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 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.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 is heavily 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 and importlib.machinery.ExtensionFileLoader.
- classmethod factory(loader)
A static method which returns a callable that creates a lazy loader. This is meant to be used in situations where the loader is passed by class instead of by instance.
suffixes = importlib.machinery.SOURCE_SUFFIXES loader = importlib.machinery.SourceFileLoader lazy_loader = importlib.util.LazyLoader.factory(loader) finder = importlib.machinery.FileFinder(path, (lazy_loader, suffixes))
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 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() (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