importlib
Brett Cannon <brett@python.org>
Brett Cannon <brett@python.org>
3.1
Source code: Lib/importlib/__init__.py
The purpose of the importlib package is three-fold.
One is to provide the implementation of the import statement (and thus, by extension, the __import__ function) in Python source code. This provides an implementation of !import which is portable to any Python interpreter. This also provides an implementation which is easier to comprehend than one implemented in a programming language other than Python.
Two, the components to implement import are exposed in this package, making it easier for users to create their own custom objects (known generically as an importer) to participate in the import process.
Three, the package contains modules exposing additional functionality for managing aspects of Python packages:
importlib.metadatapresents access to metadata from third-party distributions.importlib.resourcesprovides routines for accessing non-code "resources" from Python packages.
importThe language reference for the
importstatement.- Packages specification
Original specification of packages. Some semantics have changed since the writing of this document (e.g. redirecting based on
Noneinsys.modules).- The
.__import__function The
importstatement is syntactic sugar for this function.sys-path-initThe initialization of
sys.path.235Import on Case-Insensitive Platforms
263Defining Python Source Code Encodings
302New Import Hooks
328Imports: Multi-Line and Absolute/Relative
366Main module explicit relative imports
420Implicit namespace packages
451A ModuleSpec Type for the Import System
488Elimination of PYO files
489Multi-phase extension module initialization
552Deterministic pycs
3120Using UTF-8 as the Default Source Encoding
3147PYC Repository Directories
__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.
import_module(name, package=None)
Import a module. The name argument specifies what module to import in absolute or relative terms (e.g. either pkg.mod or ..mod). If the name is specified in relative terms, then the package argument must be set to the name of the package which is to act as the anchor for resolving the package name (e.g. import_module('..mod', 'pkg.subpkg') will import pkg.mod).
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.
3.3 Parent packages are automatically imported.
find_loader(name, path=None)
Find the loader for a module, optionally within the specified path. If the module is in sys.modules, then sys.modules[name].__loader__ is returned (unless the loader would be None or is not set, in which case ValueError is raised). Otherwise a search using sys.meta_path 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.
3.3
3.4 If __loader__ is not set, raise ValueError, just like when the attribute is set to None.
3.4 Use importlib.util.find_spec instead.
invalidate_caches()
Invalidate the internal caches of finders stored at sys.meta_path. If a finder implements invalidate_caches() then it will be called to perform the invalidation. This function should be called if any modules are created/installed while your program is running to guarantee all finders will notice the new module's existence.
3.3
3.10 Namespace packages created/installed in a different sys.path location after the same namespace was already imported are noticed.
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
loaderwhich originally loaded the module. Theinitfunction of extension modules is not called a second time. - As with all other objects in Python the old objects are only reclaimed after their reference counts drop to zero.
- The names in the module namespace are updated to point to any new or changed objects.
- Other references to the old objects (such as names external to the module) are not rebound to refer to the new objects and must be updated in each namespace where they occur if that is desired.
There are a number of other caveats:
When a module is reloaded, its dictionary (containing the module's global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem. If the new version of a module does not define a name that was defined by the old version, the old definition remains. This feature can be used to the module's advantage if it maintains a global table or cache of objects --- with a try statement it can test for the table's presence and skip its initialization if desired:
try:
cache
except NameError:
cache = {}It is generally not very useful to reload built-in or dynamically loaded modules. Reloading sys, __main__, builtins and other key modules is not recommended. In many cases extension modules are not designed to be initialized more than once, and may fail in arbitrary ways when reloaded.
If a module imports objects from another module using from ... import ..., calling reload for the other module does not redefine the objects imported from it --- one way around this is to re-execute the !from statement, another is to use !import and qualified names (module.name) instead.
If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances ---they continue to use the old class definition. The same is true for derived classes.
3.4
3.7 ModuleNotFoundError is raised when the module being reloaded lacks a ~importlib.machinery.ModuleSpec.
importlib.abc
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
+-- SourceLoaderAn abstract base class representing a finder.
3.3 Use MetaPathFinder or PathEntryFinder instead.
find_module(fullname, path=None)
An abstract method for finding a loader for the specified module. Originally specified in 302, this method was meant for use in sys.meta_path and in the path-based import subsystem.
3.4 Returns None when called instead of raising NotImplementedError.
3.10 Implement MetaPathFinder.find_spec or PathEntryFinder.find_spec instead.
An abstract base class representing a meta path finder.
3.3
3.10 No longer a subclass of Finder.
find_spec(fullname, path, target=None)
An abstract method for finding a spec <module 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.
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.
3.4 Returns None when called instead of raising NotImplementedError. Can use find_spec to provide functionality.
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.
3.4 Returns None when called instead of NotImplemented.
An abstract base class representing a path entry finder. Though it bears some similarities to MetaPathFinder, PathEntryFinder is meant for use only within the path-based import subsystem provided by importlib.machinery.PathFinder.
3.3
3.10 No longer a subclass of Finder.
find_spec(fullname, target=None)
An abstract method for finding a spec <module 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 concrete PathEntryFinders.
3.4
find_loader(fullname)
A legacy method for finding a loader for the specified module. Returns a 2-tuple of (loader, portion) where portion is a sequence of file system locations contributing to part of a namespace package. The loader may be None while specifying portion to signify the contribution of the file system locations to a namespace package. An empty list can be used for portion to signify the loader is not part of a namespace package. If loader is None and portion is the empty list then no loader or location for a namespace package were found (i.e. failure to find anything for the module).
If find_spec is defined then backwards-compatible functionality is provided.
3.4 Returns (None, []) instead of raising NotImplementedError. Uses find_spec when available to provide functionality.
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].
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.machinery.PathFinder.invalidate_caches when invalidating the caches of all cached finders.
An abstract base class for a loader. See 302 for the exact definition for a loader.
Loaders that wish to support resource reading should implement a get_resource_reader method as specified by importlib.abc.ResourceReader.
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.
3.4
3.6 This method is no longer optional when exec_module is defined.
exec_module(module)
An abstract method that executes the module in its own namespace when a module is imported or reloaded. The module should already be initialized when exec_module is called. When this method exists, create_module must be defined.
3.4
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 module's fully-qualified name. It is
'__main__'for an executed module.
__file__The location the
loaderused to load the module. For example, for modules loaded from a .py file this is the filename. It is not set on all modules (e.g. built-in modules).
__cached__The filename of a compiled version of the module's code. It is not set on all modules (e.g. built-in modules).
__path__The list of locations where the package's submodules will be found. Most of the time this is a single directory. The import system passes this attribute to
__import__()and to finders in the same way assys.pathbut just for the package. It is not set on non-package modules so it can be used as an indicator that the module is a package.
__package__The fully-qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as
__name__.
__loader__The
loaderused to load the module.
When exec_module is available then backwards-compatible functionality is provided.
3.4 Raise ImportError when called instead of NotImplementedError. Functionality provided when exec_module is available.
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 representation, as a string. The module type's default __repr__ will use the result of this method as appropriate.
3.3
3.4 Made optional instead of an abstractmethod.
3.4 The import machinery now takes care of this automatically.
importlib.machinery
Source code: Lib/importlib/machinery.py
This module contains the various objects that help import find and load modules.
SOURCE_SUFFIXES
A list of strings representing the recognized file suffixes for source modules.
3.3
DEBUG_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for non-optimized bytecode modules.
3.3
3.5 Use BYTECODE_SUFFIXES instead.
OPTIMIZED_BYTECODE_SUFFIXES
A list of strings representing the file suffixes for optimized bytecode modules.
3.3
3.5 Use BYTECODE_SUFFIXES instead.
BYTECODE_SUFFIXES
A list of strings representing the recognized file suffixes for bytecode modules (including the leading dot).
3.3
3.5 The value is no longer dependent on __debug__.
EXTENSION_SUFFIXES
A list of strings representing the recognized file suffixes for extension modules.
3.3
all_suffixes()
Returns a combined list of strings representing all file suffixes for modules recognized by the standard import machinery. This is a helper for code which simply needs to know if a filesystem path potentially refers to a module without needing any details on the kind of module (for example, inspect.getmodulename).
3.3
An importer for built-in modules. All known built-in modules are listed in sys.builtin_module_names. This class implements the importlib.abc.MetaPathFinder and importlib.abc.InspectLoader ABCs.
Only class methods are defined by this class to alleviate the need for instantiation.
3.5 As part of 489, the builtin importer now implements Loader.create_module and Loader.exec_module
An importer for frozen modules. This class implements the importlib.abc.MetaPathFinder and importlib.abc.InspectLoader ABCs.
Only class methods are defined by this class to alleviate the need for instantiation.
3.4 Gained ~Loader.create_module and ~Loader.exec_module methods.
Finder <finder> for modules declared in the Windows registry. This class implements the importlib.abc.MetaPathFinder ABC.
Only class methods are defined by this class to alleviate the need for instantiation.
3.3
3.6 Use site configuration instead. Future versions of Python may not enable this finder by default.
A Finder <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.
find_spec(fullname, path=None, target=None)
Class method that attempts to find a spec <module spec> for the module specified by fullname on sys.path or, if defined, on path. For each path entry that is searched, sys.path_importer_cache is checked. If a non-false object is found then it is used as the path entry finder to look for the module being searched for. If no entry is found in sys.path_importer_cache, then sys.path_hooks is searched for a finder for the path entry and, if found, is stored in sys.path_importer_cache along with being queried about the module. If no finder is ever found then None is both stored in the cache and returned.
3.4
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.
find_module(fullname, path=None)
A legacy wrapper around find_spec.
3.4 Use find_spec instead.
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.
3.7 Entries of None in sys.path_importer_cache are deleted.
3.4 Calls objects in sys.path_hooks with the current working directory for '' (i.e. the empty string).
A concrete implementation of importlib.abc.PathEntryFinder which caches results from the file system.
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.
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.
3.4
find_loader(fullname)
Attempt to find the loader to handle fullname within path.
3.10 Use find_spec instead.
invalidate_caches()
Clear out the internal cache.
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.
A concrete implementation of importlib.abc.SourceLoader by subclassing importlib.abc.FileLoader and providing some concrete implementations of other methods.
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.
3.6
Use importlib.abc.Loader.exec_module instead.
A concrete implementation of importlib.abc.FileLoader which can import bytecode files (i.e. no source code files exist).
Please note that direct use of bytecode files (and thus not source code files) inhibits your modules from being usable by all Python implementations or new versions of Python which change the bytecode format.
3.3
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.
3.6
Use importlib.abc.Loader.exec_module instead.
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.
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 489.
3.5
exec_module(module)
Initializes the given module object in accordance with 489.
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.
3.4
A concrete implementation of importlib.abc.InspectLoader for namespace packages. This is an alias for a private class and is only made public for introspecting the __loader__ attribute on namespace packages:
>>> from importlib.machinery import NamespaceLoader
>>> import my_namespace
>>> isinstance(my_namespace.__loader__, NamespaceLoader)
True
>>> import importlib.abc
>>> isinstance(my_namespace.__loader__, importlib.abc.Loader)
True3.11
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. For example, it is possible to update the module's __file__ at runtime and this will not be automatically reflected in the module's __spec__.origin, and vice versa.
3.4
name
(__name__)
The module's fully-qualified name. The finder should always set this attribute to a non-empty string.
loader
(__loader__)
The loader used to load the module. The finder should always set this attribute.
origin
(__file__)
The location the loader should use to load the module. For example, for modules loaded from a .py file this is the filename. The finder should always set this attribute to a meaningful value for the loader to use. In the uncommon case that there is not one (like for namespace packages), it should be set to None.
submodule_search_locations
(__path__)
The list of locations where the package's submodules will be found. Most of the time this is a single directory. The finder should set this attribute to a list, even an empty one, to indicate to the import system that the module is a package. It should be set to None for non-package modules. It is set automatically later to a special object for namespace packages.
loader_state
The finder may set this attribute to an object containing additional, module-specific data to use when loading the module. Otherwise it should be set to None.
cached
(__cached__)
The filename of a compiled version of the module's code. The finder should always set this attribute but it may be None for modules that do not need compiled code stored.
parent
(__package__)
(Read-only) The fully-qualified name of the package the module is in (or the empty string for a top-level module). If the module is a package then this is the same as name.
has_location
Trueif the spec'soriginrefers to a loadable location,Falseotherwise. This value impacts howoriginis interpreted and how the module's__file__is populated.
importlib.util
Source code: Lib/importlib/util.py
This module contains the various objects that help in the construction of an importer.
MAGIC_NUMBER
The bytes which represent the bytecode version number. If you need help with loading/writing bytecode then consider importlib.abc.SourceLoader.
3.4
cache_from_source(path, debug_override=None, *, optimization=None)
Return the 3147/488 path to the byte-compiled file associated with the source path. For example, if path is /foo/bar/baz.py the return value would be /foo/bar/__pycache__/baz.cpython-32.pyc for Python 3.2. The cpython-32 string comes from the current magic tag (see get_tag; if sys.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 of '' will result in a bytecode path of /foo/bar/__pycache__/baz.cpython-32.pyc. None causes the interpreter's optimization level to be used. Any other value's string representation is used, so /foo/bar/baz.py with an optimization of 2 will lead to the bytecode path of /foo/bar/__pycache__/baz.cpython-32.opt-2.pyc. The string representation of optimization can only be alphanumeric, else ValueError 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.
3.4
3.5 The optimization parameter was added and the debug_override parameter was deprecated.
3.6 Accepts a path-like object.
source_from_cache(path)
Given the path to a 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 3147 or 488 format, a ValueError is raised. If sys.implementation.cache_tag is not defined, NotImplementedError is raised.
3.4
3.6 Accepts a path-like object.
decode_source(source_bytes)
Decode the given bytes representing source code and return it as a string with universal newlines (as required by importlib.abc.InspectLoader.get_source).
3.4
resolve_name(name, package)
Resolve a relative module name to an absolute one.
If name has no leading dots, then name is simply returned. This allows for usage such as importlib.util.resolve_name('sys', __spec__.parent) without doing a check to see if the package argument is needed.
ImportError is raised if name is a relative module name but package is a false value (e.g. None or the empty string). ImportError is also raised if a relative name would escape its containing package (e.g. requesting ..bacon from within the spam package).
3.3
3.9 To improve consistency with import statements, raise ImportError instead of ValueError for invalid relative import attempts.
find_spec(name, package=None)
Find the spec <module spec> for a module, optionally relative to the specified package name. If the module is in sys.modules, then sys.modules[name].__spec__ is returned (unless the spec would be None or is not set, in which case ValueError is raised). Otherwise a search using sys.meta_path 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.
3.4
3.7 Raises ModuleNotFoundError instead of AttributeError if package is in fact not a package (i.e. lacks a __path__ attribute).
module_from_spec(spec)
Create a new module based on spec and spec.loader.create_module <importlib.abc.Loader.create_module>.
If spec.loader.create_module <importlib.abc.Loader.create_module> does not return None, then any pre-existing attributes will not be reset. Also, no AttributeError will be raised if triggered while accessing spec or setting an attribute on the module.
This function is preferred over using types.ModuleType to create a new module as spec is used to set as many import-controlled attributes on the module as possible.
3.5
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.
3.3 __loader__ and __package__ are automatically set (when possible).
3.4 Set __name__, __loader__ __package__ unconditionally to support reloading.
3.4 The import machinery now directly performs all the functionality provided by this function.
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.
3.4 Set __loader__ if set to None, as if the attribute does not exist.
3.4 The import machinery takes care of this automatically.
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.
3.4 The import machinery takes care of this automatically.
spec_from_loader(name, loader, *, origin=None, is_package=None)
A factory function for creating a ~importlib.machinery.ModuleSpec instance based on a loader. The parameters have the same meaning as they do for ModuleSpec. The function uses available loader APIs, such as InspectLoader.is_package, to fill in any missing information on the spec.
3.4
spec_from_file_location(name, location, *, loader=None, submodule_search_locations=None)
A factory function for creating a ~importlib.machinery.ModuleSpec instance based on the path to a file. Missing information will be filled in on the spec by making use of loader APIs and by the implication that the module will be file-based.
3.4
3.6 Accepts a path-like object.
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.
3.7
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 ~importlib.abc.Loader.exec_module as control over what module type is used for the module is required. For those same reasons, the loader's ~importlib.abc.Loader.create_module method must return None or a type for which its __class__ attribute can be mutated along with not using slots <__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.
3.5
3.6 Began calling ~importlib.abc.Loader.create_module, removing the compatibility warning for importlib.machinery.BuiltinImporter and importlib.machinery.ExtensionFileLoader.
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))To programmatically import a module, use importlib.import_module. :
import importlib
itertools = importlib.import_module('itertools')If you need to find out if a module can be imported without actually doing the import, then you should use importlib.util.find_spec.
Note that if name is a submodule (contains a dot), importlib.util.find_spec will import the parent module. :
import importlib.util
import sys
# For illustrative purposes.
name = 'itertools'
if name in sys.modules:
print(f"{name!r} already in sys.modules")
elif (spec := importlib.util.find_spec(name)) is not None:
# If you chose to perform the actual import ...
module = importlib.util.module_from_spec(spec)
sys.modules[name] = module
spec.loader.exec_module(module)
print(f"{name!r} has been imported")
else:
print(f"can't find the {name!r} module")To import a Python source file directly, use the following recipe:
import importlib.util
import sys
# For illustrative purposes.
import tokenize
file_path = tokenize.__file__
module_name = tokenize.__name__
spec = importlib.util.spec_from_file_location(module_name, file_path)
module = importlib.util.module_from_spec(spec)
sys.modules[module_name] = module
spec.loader.exec_module(module)The example below shows how to implement lazy imports:
>>> import importlib.util
>>> import sys
>>> def lazy_import(name):
... spec = importlib.util.find_spec(name)
... loader = importlib.util.LazyLoader(spec.loader)
... spec.loader = loader
... module = importlib.util.module_from_spec(spec)
... sys.modules[name] = module
... loader.exec_module(module)
... return module
...
>>> lazy_typing = lazy_import("typing")
>>> #lazy_typing is a real module object,
>>> #but it is not loaded in memory yet.
>>> lazy_typing.TYPE_CHECKING
FalseFor 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))Import itself is implemented in Python code, making it possible to expose most of the import machinery through importlib. The following helps illustrate the various APIs that importlib exposes by providing an approximate implementation of importlib.import_module:
import importlib.util
import sys
def import_module(name, package=None):
"""An approximate implementation of import."""
absolute_name = importlib.util.resolve_name(name, package)
try:
return sys.modules[absolute_name]
except KeyError:
pass
path = None
if '.' in absolute_name:
parent_name, _, child_name = absolute_name.rpartition('.')
parent_module = import_module(parent_name)
path = parent_module.__spec__.submodule_search_locations
for finder in sys.meta_path:
spec = finder.find_spec(absolute_name, path)
if spec is not None:
break
else:
msg = f'No module named {absolute_name!r}'
raise ModuleNotFoundError(msg, name=absolute_name)
module = importlib.util.module_from_spec(spec)
sys.modules[absolute_name] = module
spec.loader.exec_module(module)
if path is not None:
setattr(parent_module, child_name, module)
return module