30.6. importlib
– The implementation of import
¶
New in version 3.1.
30.6.1. 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 451
- A ModuleSpec Type for the Import System
- PEP 3120
- Using UTF-8 as the Default Source Encoding
- PEP 3147
- PYC Repository Directories
30.6.2. Functions¶
-
importlib.
__import__
(name, globals=None, locals=None, fromlist=(), level=0)¶ An implementation of the built-in
__import__()
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__()
, including requiring the package from which an import is occurring to have been previously imported (i.e., package must already be imported). The most important difference 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
).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
, 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 parent’s 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.
-
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.
30.6.3. importlib.abc
– Abstract base classes related to import¶
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
+-- PyLoader (deprecated)
+-- PyPycLoader (deprecated)
-
class
importlib.abc.
Finder
¶ An abstract base class representing a finder.
Deprecated since version 3.3: Use
MetaPathFinder
orPathEntryFinder
instead.-
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.
-
-
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_module
(fullname, path)¶ An abstract 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.
-
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
.
-
-
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.New in version 3.3.
-
find_loader
(fullname)¶ An abstract 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 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).
-
find_module
(fullname)¶ A concrete implementation of
Finder.find_module()
which is equivalent toself.find_loader(fullname)[0]
.
-
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.
-
load_module
(fullname)¶ An abstract 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. Theimportlib.util.module_for_loader()
decorator handles all of these details.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.set_package()
decorator can handle the details for__package__
.
__loader__
- The loader used to load the module. (This is not set by the built-in import machinery, but it should be set whenever a loader is used.)
-
module_repr
(module)¶ An abstract method which when implemented calculates and returns the given module’s repr, as a string.
-
-
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.
-
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.
IOError
is to be raised if the path cannot be found. The path is expected to be constructed using a module’s__file__
attribute or an item from a package’s__path__
.
-
-
class
importlib.abc.
InspectLoader
¶ An abstract base class for a loader which implements the optional PEP 302 protocol for loaders that inspect modules.
-
get_code
(fullname)¶ An abstract method to return the
code
object for a module.None
is returned if the module does not have a code object (e.g. built-in module).ImportError
is raised if loader cannot find the requested module.
-
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.
-
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.
-
-
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.-
get_filename
(fullname)¶ An abstract method that is to return the value of
__file__
for the specified module. If no path is available,ImportError
is raised.If source code is available, then the method should return the path to the source file, regardless of whether a bytecode was used to load the module.
-
-
class
importlib.abc.
FileLoader
(fullname, path)¶ An abstract base class which inherits from
ResourceLoader
andExecutionLoader
, providing concrete implementations ofResourceLoader.get_data()
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()
.
-
get_data
(path)¶ Returns the open, binary file for path.
-
-
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 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 specifed 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.
New in version 3.3.
-
path_mtime
(path)¶ Optional abstract method which returns the modification time for the specified path.
Deprecated since version 3.3: This method is deprecated in favour of
path_stats()
. You don’t have to implement it, but it is still available for compatibility purposes.
-
set_data
(path, data)¶ Optional abstract method which writes the specified bytes to a file path. Any intermediate directories which do not exist are to be created automatically.
When writing to the path fails because the path is read-only (
errno.EACCES
/PermissionError
), do not propagate the exception.
-
get_code
(fullname)¶ Concrete implementation of
InspectLoader.get_code()
.
-
load_module
(fullname)¶ Concrete implementation of
Loader.load_module()
.
-
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__
.
-
class
importlib.abc.
PyLoader
¶ An abstract base class inheriting from
ExecutionLoader
andResourceLoader
designed to ease the loading of Python source modules (bytecode is not handled; seeSourceLoader
for a source/bytecode ABC). A subclass implementing this ABC will only need to worry about exposing how the source code is stored; all other details for loading Python source code will be handled by the concrete implementations of key methods.Deprecated since version 3.2: This class has been deprecated in favor of
SourceLoader
and is slated for removal in Python 3.4. See below for how to create a subclass that is compatible with Python 3.1 onwards.If compatibility with Python 3.1 is required, then use the following idiom to implement a subclass that will work with Python 3.1 onwards (make sure to implement
ExecutionLoader.get_filename()
):try: from importlib.abc import SourceLoader except ImportError: from importlib.abc import PyLoader as SourceLoader class CustomLoader(SourceLoader): def get_filename(self, fullname): """Return the path to the source file.""" # Implement ... def source_path(self, fullname): """Implement source_path in terms of get_filename.""" try: return self.get_filename(fullname) except ImportError: return None def is_package(self, fullname): """Implement is_package by looking for an __init__ file name as returned by get_filename.""" filename = os.path.basename(self.get_filename(fullname)) return os.path.splitext(filename)[0] == '__init__'
-
source_path
(fullname)¶ An abstract method that returns the path to the source code for a module. Should return
None
if there is no source code. RaisesImportError
if the loader knows it cannot handle the module.
-
get_filename
(fullname)¶ A concrete implementation of
importlib.abc.ExecutionLoader.get_filename()
that relies onsource_path()
. Ifsource_path()
returnsNone
, thenImportError
is raised.
-
load_module
(fullname)¶ A concrete implementation of
importlib.abc.Loader.load_module()
that loads Python source code. All needed information comes from the abstract methods required by this ABC. The only pertinent assumption made by this method is that when loading a package__path__
is set to[os.path.dirname(__file__)]
.
-
get_code
(fullname)¶ A concrete implementation of
importlib.abc.InspectLoader.get_code()
that creates code objects from Python source code, by requesting the source code (usingsource_path()
andget_data()
) and compiling it with the built-incompile()
function.
-
get_source
(fullname)¶ A concrete implementation of
importlib.abc.InspectLoader.get_source()
. Usesimportlib.abc.ResourceLoader.get_data()
andsource_path()
to get the source code. It tries to guess the source encoding usingtokenize.detect_encoding()
.
-
-
class
importlib.abc.
PyPycLoader
¶ An abstract base class inheriting from
PyLoader
. This ABC is meant to help in creating loaders that support both Python source and bytecode.Deprecated since version 3.2: This class has been deprecated in favor of
SourceLoader
and to properly support PEP 3147. If compatibility is required with Python 3.1, implement bothSourceLoader
andPyLoader
; instructions on how to do so are included in the documentation forPyLoader
. Do note that this solution will not support sourceless/bytecode-only loading; only source and bytecode loading.Changed in version 3.3: Updated to parse (but not use) the new source size field in bytecode files when reading and to write out the field properly when writing.
-
source_mtime
(fullname)¶ An abstract method which returns the modification time for the source code of the specified module. The modification time should be an integer. If there is no source code, return
None
. If the module cannot be found thenImportError
is raised.
-
bytecode_path
(fullname)¶ An abstract method which returns the path to the bytecode for the specified module, if it exists. It returns
None
if no bytecode exists (yet). RaisesImportError
if the loader knows it cannot handle the module.
-
get_filename
(fullname)¶ A concrete implementation of
ExecutionLoader.get_filename()
that relies onPyLoader.source_path()
andbytecode_path()
. Ifsource_path()
returns a path, then that value is returned. Else ifbytecode_path()
returns a path, that path will be returned. If a path is not available from both methods,ImportError
is raised.
-
write_bytecode
(fullname, bytecode)¶ An abstract method which has the loader write bytecode for future use. If the bytecode is written, return
True
. ReturnFalse
if the bytecode could not be written. This method should not be called ifsys.dont_write_bytecode
is true. The bytecode argument should be a bytes string or bytes array.
-
30.6.4. importlib.machinery
– Importers and path hooks¶
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.
-
importlib.machinery.
OPTIMIZED_BYTECODE_SUFFIXES
¶ A list of strings representing the file suffixes for optimized bytecode modules.
New in version 3.3.
-
importlib.machinery.
BYTECODE_SUFFIXES
¶ A list of strings representing the recognized file suffixes for bytecode modules. Set to either
DEBUG_BYTECODE_SUFFIXES
orOPTIMIZED_BYTECODE_SUFFIXES
based on whether__debug__
is true.New in version 3.3.
-
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.
-
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.
-
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_module
(fullname, path=None)¶ Class method that attempts to find a loader 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.
-
classmethod
invalidate_caches
()¶ Calls
importlib.abc.PathEntryFinder.invalidate_caches()
on all finders stored insys.path_importer_cache
.
-
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.
-
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.
-
path_stats
(path)¶ Concrete implementation of
importlib.abc.SourceLoader.path_stats()
.
-
set_data
(path, data)¶ Concrete implementation of
importlib.abc.SourceLoader.set_data()
.
-
-
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.
-
get_source
(fullname)¶ Returns
None
as bytecode files have no source when this loader is used.
-
-
class
importlib.machinery.
ExtensionFileLoader
(fullname, path)¶ A concrete implementation of
importlib.abc.InspectLoader
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.
-
load_module
(fullname)¶ Loads the extension module if and only if fullname is the same as
name
or isNone
.
-
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.
-
30.6.5. importlib.util
– Utility code for importers¶
This module contains the various objects that help in the construction of an importer.
-
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.
module_for_loader
¶ A decorator for a loader method, 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 with its__name__
attribute set to name,__loader__
set to self, and__package__
set ifimportlib.abc.InspectLoader.is_package()
is defined for self and does not raiseImportError
for name. If a new module is not needed then the module found insys.modules
will be passed into the method.If an exception is raised by the decorated method and a module was added to
sys.modules
it 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.Use of this decorator handles all the details of which module object a loader should initialize as specified by PEP 302 as best as possible.
Changed in version 3.3:
__loader__
and__package__
are automatically set (when possible).
-
@
importlib.util.
set_loader
¶ Note
It is recommended that
module_for_loader()
be used over this decorator as it subsumes this functionality.
-
@
importlib.util.
set_package
¶ A decorator for a loader to set the
__package__
attribute on the module returned by the loader. If__package__
is set and has a value other thanNone
it will not be changed. Note that the module returned by the loader is what has the attribute set on and not the module found insys.modules
.Reliance on this decorator is discouraged when it is possible to set
__package__
before importing. By setting it beforehand the code for the module is executed with the attribute set and thus can be used by global level code during initialization.Note
It is recommended that
module_for_loader()
be used over this decorator as it subsumes this functionality.