31.5. importlib
— The implementation of import
New in version 3.1.
Source code: Lib/importlib/__init__.py
31.5.1. 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
insys.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 3120
- Using UTF-8 as the Default Source Encoding
- PEP 3147
- PYC Repository Directories
31.5.2. 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 fromimportlib.__import__()
. The most important difference between these two functions is thatimport_module()
returns the specified package or module (e.g.pkg.mod
), while__import__()
returns the top-level package or module (e.g.pkg
).If you are dynamically importing a module that was created since the interpreter began execution (e.g., created a Python source file), you may need to call
invalidate_caches()
in order for the new module to be noticed by the import system.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
, thensys.modules[name].__loader__
is returned (unless the loader would beNone
or is not set, in which caseValueError
is raised). Otherwise a search usingsys.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, raiseValueError
, 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 implementsinvalidate_caches()
then it will be called to perform the invalidation. This function should be called if any modules are created/installed while your program is running to guarantee all finders will notice the new module’s existence.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
…, callingreload()
for the other module does not redefine the objects imported from it — one way around this is to re-execute thefrom
statement, another is to useimport
and qualified names (module.name) instead.If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances — they continue to use the old class definition. The same is true for derived classes.
New in version 3.4.
- 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
31.5.3. importlib.abc
– Abstract base classes related to import
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
orPathEntryFinder
instead.-
abstractmethod
find_module
(fullname, path=None) An abstact 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
.
-
abstractmethod
-
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.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 usefind_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 onsys.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 ofFinder
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.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 raisingNotImplementedError
. Usesfind_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.
-
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 intosys.modules
before any loading begins, to prevent recursion from the import. If the loader inserted a module and the load fails, it must be removed by the loader fromsys.modules
; modules already insys.modules
before the loader began execution should be left alone (seeimportlib.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 parent package for the module/package. If the module is
top-level then it has a value of the empty string. 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 ofNotImplementedError
. Functionality provided whenexec_module()
is available.Deprecated since version 3.4: The recommended API for loading a module is
exec_module()
(andcreate_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.
ResourceLoader
An abstract base class for a loader which implements the optional PEP 302 protocol for loading arbitrary resources from the storage back-end.
-
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__
.Changed in version 3.4: Raises
OSError
instead ofNotImplementedError
.
-
abstractmethod
-
class
importlib.abc.
InspectLoader
An abstract base class for a loader which implements the optional PEP 302 protocol for loaders that inspect modules.
-
get_code
(fullname) Return the code object for a module, or
None
if the module does not have a code object (as would be the case, for example, for a built-in module). Raise anImportError
if loader cannot find the requested module.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. ReturnsNone
if no source is available (e.g. a built-in module). RaisesImportError
if the loader cannot find the module specified.Changed in version 3.4: Raises
ImportError
instead ofNotImplementedError
.
-
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 the loader cannot find the module.Changed in version 3.4: Raises
ImportError
instead ofNotImplementedError
.
-
static
source_to_code
(data, path='<string>') Create a code object from Python source.
The data argument can be whatever the
compile()
function supports (i.e. string or bytes). The path argument should be the “path” to where the source code originated from, which can be an abstract concept (e.g. location in a zip file).With the subsequent code object one can execute it in a module by running
exec(code, module.__dict__)
.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.
Changed in version 3.4: Raises
ImportError
instead ofNotImplementedError
.
-
abstractmethod
-
class
importlib.abc.
FileLoader
(fullname, path) An abstract base class which inherits from
ResourceLoader
andExecutionLoader
, providing concrete implementations ofResourceLoader.get_data()
andExecutionLoader.get_filename()
.The fullname argument is a fully resolved name of the module the loader is to handle. The path argument is the path to the file for the module.
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.
Changed in version 3.4: Raise
OSError
instead ofNotImplementedError
.
-
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. RaiseOSError
if the path cannot be handled.Changed in version 3.4: Raise
OSError
instead ofNotImplementedError
.
-
set_data
(path, data) Optional abstract method which writes the specified bytes to a file path. Any intermediate directories which do not exist are to be created automatically.
When writing to the path fails because the path is read-only (
errno.EACCES
/PermissionError
), do not propagate the exception.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 byExecutionLoader.get_filename()
) is a file named__init__
when the file extension is removed and the module name itself does not end in__init__
.
31.5.4. importlib.machinery
– Importers and path hooks
Source code: 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 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 implements
Loader.create_module()
andLoader.exec_module()
-
class
importlib.machinery.
FrozenImporter
An importer for frozen modules. This class implements the
importlib.abc.MetaPathFinder
andimportlib.abc.InspectLoader
ABCs.Only class methods are defined by this class to alleviate the need for instantiation.
-
class
importlib.machinery.
WindowsRegistryFinder
Finder for modules declared in the Windows registry. This class implements the
importlib.abc.Finder
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 theimportlib.abc.MetaPathFinder
ABC.Only class methods are defined by this class to alleviate the need for instantiation.
-
classmethod
find_spec
(fullname, path=None, target=None) Class method that attempts to find a spec for the module specified by fullname on
sys.path
or, if defined, on path. For each path entry that is searched,sys.path_importer_cache
is checked. If a non-false object is found then it is used as the path entry finder to look for the module being searched for. If no entry is found insys.path_importer_cache
, thensys.path_hooks
is searched for a finder for the path entry and, if found, is stored insys.path_importer_cache
along with being queried about the module. If no finder is ever found thenNone
is both stored in the cache and returned.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 insys.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 insys.path_importer_cache
.
Changed in version 3.4: Calls objects in
sys.path_hooks
with the current working directory for''
(i.e. the empty string).-
classmethod
-
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 ofFileFinder
is returned by the closure using the path argument given to the closure directly and loader_details indirectly.If the argument to the closure is not an existing directory,
ImportError
is raised.
-
-
class
importlib.machinery.
SourceFileLoader
(fullname, path) A concrete implementation of
importlib.abc.SourceLoader
by subclassingimportlib.abc.FileLoader
and providing some concrete implementations of other methods.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 onEXTENSION_SUFFIXES
.
-
get_code
(fullname) Returns
None
as extension modules lack a code object.
-
get_source
(fullname) Returns
None
as extension modules do not have source code.
-
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.
New in version 3.4.
-
name
(
__name__
)A string for the fully-qualified name of the module.
-
loader
(
__loader__
)The loader to use for loading. For namespace packages this should be set to
None
.-
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.-
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) Fully-qualified name of the package to which the module belongs as a submodule (or
None
).-
has_location
Boolean indicating whether or not the module’s “origin” attribute refers to a loadable location.
-
31.5.5. 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. Thecpython-32
string comes from the current magic tag (seeget_tag()
; ifsys.implementation.cache_tag
is not defined thenNotImplementedError
will be raised).The optimization parameter is used to specify the optimization level of the bytecode file. An empty string represents no optimization, so
/foo/bar/baz.py
with an optimization of''
will result in a bytecode path of/foo/bar/__pycache__/baz.cpython-32.pyc
.None
causes the interpter’s optimization level to be used. Any other value’s string representation being used, so/foo/bar/baz.py
with an optimization of2
will lead to the bytecode path of/foo/bar/__pycache__/baz.cpython-32.opt-2.pyc
. The string representation of optimization can only be alphanumeric, elseValueError
is raised.The debug_override parameter is deprecated and can be used to override the system’s value for
__debug__
. ATrue
value is the equivalent of setting optimization to the empty string. AFalse
value is the same as setting optimization to1
. If both debug_override an optimization are notNone
thenTypeError
is raised.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, aValueError
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', __package__)
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 thespam
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
, thensys.modules[name].__spec__
is returned (unless the spec would beNone
or is not set, in which caseValueError
is raised). Otherwise a search usingsys.meta_path
is done.None
is returned if no spec is found.If name is for a submodule (contains a dot), the parent module is automatically imported.
name and package work the same as for
import_module()
.New in version 3.4.
-
importlib.util.
module_from_spec
(spec) Create a new module based on spec and
spec.loader.create_module
.If
spec.loader.create_module
does not returnNone
, then any pre-existing attributes will not be reset. Also, noAttributeError
will be raised if triggered while accessing spec or setting an attribute on the module.This function is preferred over using
types.ModuleType
to create a new module as spec is used to set as many import-controlled attributes on the module as possible.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 whatimportlib.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 insys.modules
. If the module was already insys.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 thanNone
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.
-
class
importlib.util.
LazyLoader
(loader) A class which postpones the execution of the loader of a module until the module has an attribute accessed.
This class only works with loaders that define
exec_module()
as control over what module type is used for the module is required. For those same reasons, the loader’screate_module()
method must returnNone
or a type for which its__class__
attribute can be mutated along with not using slots. Finally, modules which substitute the object placed intosys.modules
will not work as there is no way to properly replace the module references throughout the interpreter safely;ValueError
is raised if such a substitution is detected.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 forimportlib.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))
-
classmethod
31.5.6. Examples
31.5.6.1. Importing programmatically
To programmatically import a module, use importlib.import_module()
.
import importlib
itertools = importlib.import_module('itertools')
31.5.6.2. 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'
spec = importlib.util.find_spec(name)
if spec is None:
print("can't find the itertools module")
else:
# If you chose to perform the actual import ...
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
# Adding the module to sys.modules is optional.
sys.modules[name] = module
31.5.6.3. Importing a source file directly
To import a Python source file directly, use the following recipe (Python 3.4 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)
spec.loader.exec_module(module)
# Optional; only necessary if you want to be able to import the module
# by name later.
sys.modules[module_name] = module
31.5.6.4. 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))
31.5.6.5. 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:
raise ImportError(f'No module named {absolute_name!r}')
module = importlib.util.module_from_spec(spec)
spec.loader.exec_module(module)
sys.modules[absolute_name] = module
if path is not None:
setattr(parent_module, child_name, module)
return module