| Python 3.6.5 Documentation > "importlib" — The implementation of "import"
"importlib" — The implementation of "import"
********************************************
New in version 3.1.
**Source code:** Lib/importlib/__init__.py
======================================================================
Introduction
============
The purpose of the "importlib" package is two-fold. One is to provide
the implementation of the "import" statement (and thus, by extension,
the "__import__()" function) in Python source code. This provides an
implementation of "import" which is portable to any Python
interpreter. This also provides an implementation which is easier to
comprehend than one implemented in a programming language other than
Python.
Two, the components to implement "import" are exposed in this package,
making it easier for users to create their own custom objects (known
generically as an *importer*) to participate in the import process.
See also:
The import statement
The language reference for the "import" statement.
Packages specification
Original specification of packages. Some semantics have changed
since the writing of this document (e.g. redirecting based on
"None" in "sys.modules").
The "__import__()" function
The "import" statement is syntactic sugar for this function.
**PEP 235**
Import on Case-Insensitive Platforms
**PEP 263**
Defining Python Source Code Encodings
**PEP 302**
New Import Hooks
**PEP 328**
Imports: Multi-Line and Absolute/Relative
**PEP 366**
Main module explicit relative imports
**PEP 420**
Implicit namespace packages
**PEP 451**
A ModuleSpec Type for the Import System
**PEP 488**
Elimination of PYO files
**PEP 489**
Multi-phase extension module initialization
**PEP 3120**
Using UTF-8 as the Default Source Encoding
**PEP 3147**
PYC Repository Directories
Functions
=========
importlib.__import__(name, globals=None, locals=None, fromlist=(), level=0)
An implementation of the built-in "__import__()" function.
Note: Programmatic importing of modules should use
"import_module()" instead of this function.
importlib.import_module(name, package=None)
Import a module. The *name* argument specifies what module to
import in absolute or relative terms (e.g. either "pkg.mod" or
"..mod"). If the name is specified in relative terms, then the
*package* argument must be set to the name of the package which is
to act as the anchor for resolving the package name (e.g.
"import_module('..mod', 'pkg.subpkg')" will 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.
Changed in version 3.3: Parent packages are automatically imported.
importlib.find_loader(name, path=None)
Find the loader for a module, optionally within the specified
*path*. If the module is in "sys.modules", then
"sys.modules[name].__loader__" is returned (unless the loader would
be "None" or is not set, in which case "ValueError" is raised).
Otherwise a search using "sys.meta_path" is done. "None" is
returned if no loader is found.
A dotted name does not have its parents implicitly imported as that
requires loading them and that may not be desired. To properly
import a submodule you will need to import all parent packages of
the submodule and use the correct argument to *path*.
New in version 3.3.
Changed in version 3.4: If "__loader__" is not set, raise
"ValueError", just like when the attribute is set to "None".
Deprecated since version 3.4: Use "importlib.util.find_spec()"
instead.
importlib.invalidate_caches()
Invalidate the internal caches of finders stored at
"sys.meta_path". If a finder implements "invalidate_caches()" then
it will be called to perform the invalidation. This function
should be called if any modules are created/installed while your
program is running to guarantee all finders will notice the new
module’s existence.
New in version 3.3.
importlib.reload(module)
Reload a previously imported *module*. The argument must be a
module object, so it must have been successfully imported before.
This is useful if you have edited the module source file using an
external editor and want to try out the new version without leaving
the Python interpreter. The return value is the module object
(which can be different if re-importing causes a different object
to be placed in "sys.modules").
When "reload()" is executed:
* Python module’s code is recompiled and the module-level code
re- executed, defining a new set of objects which are bound to
names in the module’s dictionary by reusing the *loader* which
originally loaded the module. The "init" function of extension
modules is not called a second time.
* As with all other objects in Python the old objects are only
reclaimed after their reference counts drop to zero.
* The names in the module namespace are updated to point to any
new or changed objects.
* Other references to the old objects (such as names external to
the module) are not rebound to refer to the new objects and must
be updated in each namespace where they occur if that is desired.
There are a number of other caveats:
When a module is reloaded, its dictionary (containing the module’s
global variables) is retained. Redefinitions of names will
override the old definitions, so this is generally not a problem.
If the new version of a module does not define a name that was
defined by the old version, the old definition remains. This
feature can be used to the module’s advantage if it maintains a
global table or cache of objects — with a "try" statement it can
test for the table’s presence and skip its initialization if
desired:
try:
cache
except NameError:
cache = {}
It is generally not very useful to reload built-in or dynamically
loaded modules. Reloading "sys", "__main__", "builtins" and other
key modules is not recommended. In many cases extension modules
are not designed to be initialized more than once, and may fail in
arbitrary ways when reloaded.
If a module imports objects from another module using "from" …
"import" …, calling "reload()" for the other module does not
redefine the objects imported from it — one way around this is to
re-execute the "from" statement, another is to 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.
New in version 3.4.
"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" or
"PathEntryFinder" 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
raising "NotImplementedError".
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
raising "NotImplementedError". Can use "find_spec()" to provide
functionality.
Deprecated since version 3.4: Use "find_spec()" instead.
invalidate_caches()
An optional method which, when called, should invalidate any
internal cache used by the finder. Used by
"importlib.invalidate_caches()" when invalidating the caches of
all finders on "sys.meta_path".
Changed in version 3.4: Returns "None" when called instead of
"NotImplemented".
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 by "PathFinder". This ABC is a subclass of "Finder" for
compatibility reasons only.
New in version 3.3.
find_spec(fullname, target=None)
An abstract method for finding a *spec* for the specified
module. The finder will search for the module only within the
*path entry* to which it is assigned. If a spec cannot be
found, "None" is returned. When passed in, "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)" 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.
Changed in version 3.4: Returns "(None, [])" instead of raising
"NotImplementedError". Uses "find_spec()" when available to
provide functionality.
Deprecated since version 3.4: Use "find_spec()" instead.
find_module(fullname)
A concrete implementation of "Finder.find_module()" which is
equivalent to "self.find_loader(fullname)[0]".
Deprecated since version 3.4: Use "find_spec()" instead.
invalidate_caches()
An optional method which, when called, should invalidate any
internal cache used by the finder. Used by
"PathFinder.invalidate_caches()" when invalidating the caches of
all cached finders.
class importlib.abc.Loader
An abstract base class for a *loader*. See **PEP 302** for the
exact definition for a loader.
create_module(spec)
A method that returns the module object to use when importing a
module. This method may return "None", indicating that default
module creation semantics should take place.
New in version 3.4.
Changed in version 3.5: Starting in Python 3.6, this method will
not be optional when "exec_module()" is defined.
exec_module(module)
An abstract method that executes the module in its own namespace
when a module is imported or reloaded. The module should
already be initialized when "exec_module()" is called. When this
method exists, "create_module()" must be defined.
New in version 3.4.
Changed in version 3.6: "create_module()" must also be defined.
load_module(fullname)
A legacy method for loading a module. If the module cannot be
loaded, "ImportError" is raised, otherwise the loaded module is
returned.
If the requested module already exists in "sys.modules", that
module should be used and reloaded. Otherwise the loader should
create a new module and insert it into "sys.modules" before any
loading begins, to prevent recursion from the import. If the
loader inserted a module and the load fails, it must be removed
by the loader from "sys.modules"; modules already in
"sys.modules" before the loader began execution should be left
alone (see "importlib.util.module_for_loader()").
The loader should set several attributes on the module. (Note
that some of these attributes can change when a module is
reloaded):
* "__name__"
The name of the module.
* "__file__"
The path to where the module data is stored (not set for
built-in modules).
* "__cached__"
The path to where a compiled version of the module
is/should be stored (not set when the attribute would be
inappropriate).
* "__path__"
A list of strings specifying the search path within a
package. This attribute is not set on modules.
* "__package__"
The 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
of "NotImplementedError". Functionality provided when
"exec_module()" is available.
Deprecated since version 3.4: The recommended API for loading a
module is "exec_module()" (and "create_module()"). Loaders
should implement it instead of load_module(). The import
machinery takes care of all the other responsibilities of
load_module() when exec_module() is implemented.
module_repr(module)
A legacy method which when implemented calculates and returns
the given module’s repr, as a string. The module type’s default
repr() will use the result of this method as appropriate.
New in version 3.3.
Changed in version 3.4: Made optional instead of an
abstractmethod.
Deprecated since version 3.4: The import machinery now takes
care of this automatically.
class importlib.abc.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 of
"NotImplementedError".
class importlib.abc.InspectLoader
An abstract base class for a *loader* which implements the optional
**PEP 302** protocol for loaders that inspect modules.
get_code(fullname)
Return the code object for a module, or "None" if the module
does not have a code object (as would be the case, for example,
for a built-in module). Raise an "ImportError" if loader cannot
find the requested module.
Note: While the method has a default implementation, it is
suggested that it be overridden if possible for performance.
Changed in version 3.4: No longer abstract and a concrete
implementation is provided.
abstractmethod get_source(fullname)
An abstract method to return the source of a module. It is
returned as a text string using *universal newlines*,
translating all recognized line separators into "'\n'"
characters. Returns "None" if no source is available (e.g. a
built-in module). Raises "ImportError" if the loader cannot find
the module specified.
Changed in version 3.4: Raises "ImportError" instead of
"NotImplementedError".
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 of
"NotImplementedError".
static source_to_code(data, path='<string>')
Create a code object from Python source.
The *data* argument can be whatever the "compile()" function
supports (i.e. string or bytes). The *path* argument should be
the “path” to where the source code originated from, which can
be an abstract concept (e.g. location in a zip file).
With the subsequent code object one can execute it in a module
by running "exec(code, module.__dict__)".
New in version 3.4.
Changed in version 3.5: Made the method static.
exec_module(module)
Implementation of "Loader.exec_module()".
New in version 3.4.
load_module(fullname)
Implementation of "Loader.load_module()".
Deprecated since version 3.4: use "exec_module()" instead.
class importlib.abc.ExecutionLoader
An abstract base class which inherits from "InspectLoader" that,
when implemented, helps a module to be executed as a script. The
ABC represents an optional **PEP 302** protocol.
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 of
"NotImplementedError".
class importlib.abc.FileLoader(fullname, path)
An abstract base class which inherits from "ResourceLoader" and
"ExecutionLoader", providing concrete implementations of
"ResourceLoader.get_data()" and "ExecutionLoader.get_filename()".
The *fullname* argument is a fully resolved name of the module the
loader is to handle. The *path* argument is the path to the file
for the module.
New in version 3.3.
name
The name of the module the loader can handle.
path
Path to the file of the module.
load_module(fullname)
Calls super’s "load_module()".
Deprecated since version 3.4: Use "Loader.exec_module()"
instead.
abstractmethod get_filename(fullname)
Returns "path".
abstractmethod get_data(path)
Reads *path* as a binary file and returns the bytes from it.
class importlib.abc.SourceLoader
An abstract base class for implementing source (and optionally
bytecode) file loading. The class inherits from both
"ResourceLoader" and "ExecutionLoader", requiring the
implementation of:
* "ResourceLoader.get_data()"
* "ExecutionLoader.get_filename()"
Should only return the path to the source file; sourceless
loading is not supported.
The abstract methods defined by this class are to add optional
bytecode file support. Not implementing these optional methods (or
causing them to raise "NotImplementedError") causes the loader to
only work with source code. Implementing the methods allows the
loader to work with source *and* bytecode files; it does not allow
for *sourceless* loading where only bytecode is provided. Bytecode
files are an optimization to speed up loading by removing the
parsing step of Python’s compiler, and so no bytecode-specific API
is exposed.
path_stats(path)
Optional abstract method which returns a "dict" containing
metadata about the specified path. Supported dictionary keys
are:
* "'mtime'" (mandatory): an integer or floating-point number
representing the modification time of the source code;
* "'size'" (optional): the size in bytes of the source code.
Any other keys in the dictionary are ignored, to allow for
future extensions. If the path cannot be handled, "OSError" is
raised.
New in version 3.3.
Changed in version 3.4: Raise "OSError" instead of
"NotImplementedError".
path_mtime(path)
Optional abstract method which returns the modification time for
the specified path.
Deprecated since version 3.3: This method is deprecated in
favour of "path_stats()". You don’t have to implement it, but
it is still available for compatibility purposes. Raise
"OSError" if the path cannot be handled.
Changed in version 3.4: Raise "OSError" instead of
"NotImplementedError".
set_data(path, data)
Optional abstract method which writes the specified bytes to a
file path. Any intermediate directories which do not exist are
to be created automatically.
When writing to the path fails because the path is read-only
("errno.EACCES"/"PermissionError"), do not propagate the
exception.
Changed in version 3.4: No longer raises "NotImplementedError"
when called.
get_code(fullname)
Concrete implementation of "InspectLoader.get_code()".
exec_module(module)
Concrete implementation of "Loader.exec_module()".
New in version 3.4.
load_module(fullname)
Concrete implementation of "Loader.load_module()".
Deprecated since version 3.4: Use "exec_module()" instead.
get_source(fullname)
Concrete implementation of "InspectLoader.get_source()".
is_package(fullname)
Concrete implementation of "InspectLoader.is_package()". A
module is determined to be a package if its file path (as
provided by "ExecutionLoader.get_filename()") is a file named
"__init__" when the file extension is removed **and** the module
name itself does not end in "__init__".
"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 the
"importlib.abc.MetaPathFinder" and "importlib.abc.InspectLoader"
ABCs.
Only class methods are defined by this class to alleviate the need
for instantiation.
Changed in version 3.5: As part of **PEP 489**, the builtin
importer now implements "Loader.create_module()" and
"Loader.exec_module()"
class importlib.machinery.FrozenImporter
An *importer* for frozen modules. This class implements the
"importlib.abc.MetaPathFinder" and "importlib.abc.InspectLoader"
ABCs.
Only class methods are defined by this class to alleviate the need
for instantiation.
class importlib.machinery.WindowsRegistryFinder
*Finder* for modules declared in the Windows registry. This class
implements the "importlib.abc.MetaPathFinder" ABC.
Only class methods are defined by this class to alleviate the need
for instantiation.
New in version 3.3.
Deprecated since version 3.6: Use "site" configuration instead.
Future versions of Python may not enable this finder by default.
class importlib.machinery.PathFinder
A *Finder* for "sys.path" and package "__path__" attributes. This
class implements the "importlib.abc.MetaPathFinder" ABC.
Only class methods are defined by this class to alleviate the need
for instantiation.
classmethod find_spec(fullname, path=None, target=None)
Class method that attempts to find a *spec* for the module
specified by *fullname* on "sys.path" or, if defined, on *path*.
For each path entry that is searched, "sys.path_importer_cache"
is checked. If a non-false object is found then it is used as
the *path entry finder* to look for the module being searched
for. If no entry is found in "sys.path_importer_cache", then
"sys.path_hooks" is searched for a finder for the path entry
and, if found, is stored in "sys.path_importer_cache" along with
being queried about the module. If no finder is ever found then
"None" is both stored in the cache and returned.
New in version 3.4.
Changed in version 3.5: If the current working directory –
represented by an empty string – is no longer valid then "None"
is returned but no value is cached in "sys.path_importer_cache".
classmethod find_module(fullname, path=None)
A legacy wrapper around "find_spec()".
Deprecated since version 3.4: Use "find_spec()" instead.
classmethod invalidate_caches()
Calls "importlib.abc.PathEntryFinder.invalidate_caches()" on all
finders stored in "sys.path_importer_cache".
Changed in version 3.4: Calls objects in "sys.path_hooks" with the
current working directory for "''" (i.e. the empty string).
class importlib.machinery.FileFinder(path, *loader_details)
A concrete implementation of "importlib.abc.PathEntryFinder" which
caches results from the file system.
The *path* argument is the directory for which the finder is in
charge of searching.
The *loader_details* argument is a variable number of 2-item tuples
each containing a loader and a sequence of file suffixes the loader
recognizes. The loaders are expected to be callables which accept
two arguments of the module’s name and the path to the file found.
The finder will cache the directory contents as necessary, making
stat calls for each module search to verify the cache is not
outdated. Because cache staleness relies upon the granularity of
the operating system’s state information of the file system, there
is a potential race condition of searching for a module, creating a
new file, and then searching for the module the new file
represents. If the operations happen fast enough to fit within the
granularity of stat calls, then the module search will fail. To
prevent this from happening, when you create a module dynamically,
make sure to call "importlib.invalidate_caches()".
New in version 3.3.
path
The path the finder will search in.
find_spec(fullname, target=None)
Attempt to find the spec to handle *fullname* within "path".
New in version 3.4.
find_loader(fullname)
Attempt to find the loader to handle *fullname* within "path".
invalidate_caches()
Clear out the internal cache.
classmethod path_hook(*loader_details)
A class method which returns a closure for use on
"sys.path_hooks". An instance of "FileFinder" is returned by the
closure using the path argument given to the closure directly
and *loader_details* indirectly.
If the argument to the closure is not an existing directory,
"ImportError" is raised.
class importlib.machinery.SourceFileLoader(fullname, path)
A concrete implementation of "importlib.abc.SourceLoader" by
subclassing "importlib.abc.FileLoader" and providing some concrete
implementations of other methods.
New in version 3.3.
name
The name of the module that this loader will handle.
path
The path to the source file.
is_package(fullname)
Return true if "path" appears to be for a package.
path_stats(path)
Concrete implementation of
"importlib.abc.SourceLoader.path_stats()".
set_data(path, data)
Concrete implementation of
"importlib.abc.SourceLoader.set_data()".
load_module(name=None)
Concrete implementation of "importlib.abc.Loader.load_module()"
where specifying the name of the module to load is optional.
Deprecated since version 3.6: Use
"importlib.abc.Loader.exec_module()" instead.
class importlib.machinery.SourcelessFileLoader(fullname, path)
A concrete implementation of "importlib.abc.FileLoader" which can
import bytecode files (i.e. no source code files exist).
Please note that direct use of bytecode files (and thus not source
code files) inhibits your modules from being usable by all Python
implementations or new versions of Python which change the bytecode
format.
New in version 3.3.
name
The name of the module the loader will handle.
path
The path to the bytecode file.
is_package(fullname)
Determines if the module is a package based on "path".
get_code(fullname)
Returns the code object for "name" created from "path".
get_source(fullname)
Returns "None" as bytecode files have no source when this loader
is used.
load_module(name=None)
Concrete implementation of "importlib.abc.Loader.load_module()"
where specifying the name of the module to load is optional.
Deprecated since version 3.6: Use
"importlib.abc.Loader.exec_module()" instead.
class importlib.machinery.ExtensionFileLoader(fullname, path)
A concrete implementation of "importlib.abc.ExecutionLoader" for
extension modules.
The *fullname* argument specifies the name of the module the loader
is to support. The *path* argument is the path to the extension
module’s file.
New in version 3.3.
name
Name of the module the loader supports.
path
Path to the extension module.
create_module(spec)
Creates the module object from the given specification in
accordance with **PEP 489**.
New in version 3.5.
exec_module(module)
Initializes the given module object in accordance with **PEP
489**.
New in version 3.5.
is_package(fullname)
Returns "True" if the file path points to a package’s "__init__"
module based on "EXTENSION_SUFFIXES".
get_code(fullname)
Returns "None" as extension modules lack a code object.
get_source(fullname)
Returns "None" as extension modules do not have source code.
get_filename(fullname)
Returns "path".
New in version 3.4.
class importlib.machinery.ModuleSpec(name, loader, *, origin=None, loader_state=None, is_package=None)
A specification for a module’s import-system-related state. This
is typically exposed as the module’s "__spec__" attribute. In the
descriptions below, the names in parentheses give the corresponding
attribute available directly on the module object. E.g.
"module.__spec__.origin == module.__file__". Note however that
while the *values* are usually equivalent, they can differ since
there is no synchronization between the two objects. Thus it is
possible to update the module’s "__path__" at runtime, and this
will not be automatically reflected in
"__spec__.submodule_search_locations".
New in version 3.4.
name
("__name__")
A string for the fully-qualified name of the module.
loader
("__loader__")
The loader 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.
"importlib.util" – Utility code for importers
=============================================
**Source code:** Lib/importlib/util.py
======================================================================
This module contains the various objects that help in the construction
of an *importer*.
importlib.util.MAGIC_NUMBER
The bytes which represent the bytecode version number. If you need
help with loading/writing bytecode then consider
"importlib.abc.SourceLoader".
New in version 3.4.
importlib.util.cache_from_source(path, debug_override=None, *, optimization=None)
Return the **PEP 3147**/**PEP 488** path to the byte-compiled file
associated with the source *path*. For example, if *path* is
"/foo/bar/baz.py" the return value would be
"/foo/bar/__pycache__/baz.cpython-32.pyc" for Python 3.2. The
"cpython-32" string comes from the current magic tag (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
interpter’s optimization level to be used. Any other value’s string
representation being 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.
New in version 3.4.
Changed in version 3.5: The *optimization* parameter was added and
the *debug_override* parameter was deprecated.
Changed in version 3.6: Accepts a *path-like object*.
importlib.util.source_from_cache(path)
Given the *path* to a **PEP 3147** file name, return the associated
source code file path. For example, if *path* is
"/foo/bar/__pycache__/baz.cpython-32.pyc" the returned path would
be "/foo/bar/baz.py". *path* need not exist, however if it does
not conform to **PEP 3147** or **PEP 488** format, a "ValueError"
is raised. If "sys.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 the
"spam" package).
New in version 3.3.
importlib.util.find_spec(name, package=None)
Find the *spec* for a module, optionally relative to the specified
**package** name. If the module is in "sys.modules", then
"sys.modules[name].__spec__" is returned (unless the spec would 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()".
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 return "None", then any
pre-existing attributes will not be reset. Also, no
"AttributeError" will be raised if triggered while accessing
**spec** or setting an attribute on the module.
This function is preferred over using "types.ModuleType" to create
a new module as **spec** is used to set as many import-controlled
attributes on the module as possible.
New in version 3.5.
@importlib.util.module_for_loader
A *decorator* for "importlib.abc.Loader.load_module()" to handle
selecting the proper module object to load with. The decorated
method is expected to have a call signature taking two positional
arguments (e.g. "load_module(self, module)") for which the second
argument will be the module **object** to be used by the loader.
Note that the decorator will not work on static methods because of
the assumption of two arguments.
The decorated method will take in the **name** of the module to be
loaded as expected for a *loader*. If the module is not found in
"sys.modules" then a new one is constructed. Regardless of where
the module came from, "__loader__" set to **self** and
"__package__" is set based on what
"importlib.abc.InspectLoader.is_package()" returns (if available).
These attributes are set unconditionally to support reloading.
If an exception is raised by the decorated method and a module was
added to "sys.modules", then the module will be removed to prevent
a partially initialized module from being in left in "sys.modules".
If the module was already in "sys.modules" then it is left alone.
Changed in version 3.3: "__loader__" and "__package__" are
automatically set (when possible).
Changed in version 3.4: Set "__name__", "__loader__" "__package__"
unconditionally to support reloading.
Deprecated since version 3.4: The import machinery now directly
performs all the functionality provided by this function.
@importlib.util.set_loader
A *decorator* for "importlib.abc.Loader.load_module()" to set the
"__loader__" attribute on the returned module. If the attribute is
already set the decorator does nothing. It is assumed that the
first positional argument to the wrapped method (i.e. "self") is
what "__loader__" should be set to.
Changed in version 3.4: Set "__loader__" if set to "None", as if
the attribute does not exist.
Deprecated since version 3.4: The import machinery takes care of
this automatically.
@importlib.util.set_package
A *decorator* for "importlib.abc.Loader.load_module()" to set the
"__package__" attribute on the returned module. If "__package__" is
set and has a value other than "None" it will not be changed.
Deprecated since version 3.4: The import machinery takes care of
this automatically.
importlib.util.spec_from_loader(name, loader, *, origin=None, is_package=None)
A factory function for creating a "ModuleSpec" instance based on a
loader. The parameters have the same meaning as they do for
ModuleSpec. The function uses available *loader* APIs, such as
"InspectLoader.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’s "create_module()"
method must return "None" or a type for which its "__class__"
attribute can be mutated along with not using *slots*. Finally,
modules which substitute the object placed into "sys.modules" will
not work as there is no way to properly replace the module
references throughout the interpreter safely; "ValueError" is
raised if such a substitution is detected.
Note: For projects where startup time is critical, this class
allows for potentially minimizing the cost of loading a module if
it is never used. For projects where startup time is not
essential then use of this class is **heavily** discouraged due
to error messages created during loading being postponed and thus
occurring out of context.
New in version 3.5.
Changed in version 3.6: Began calling "create_module()", removing
the compatibility warning for "importlib.machinery.BuiltinImporter"
and "importlib.machinery.ExtensionFileLoader".
classmethod factory(loader)
A static method which returns a callable that creates a lazy
loader. This is meant to be used in situations where the loader
is passed by class instead of by instance.
suffixes = importlib.machinery.SOURCE_SUFFIXES
loader = importlib.machinery.SourceFileLoader
lazy_loader = importlib.util.LazyLoader.factory(loader)
finder = importlib.machinery.FileFinder(path, (lazy_loader, suffixes))
Examples
========
Importing programmatically
--------------------------
To programmatically import a module, use "importlib.import_module()".
import importlib
itertools = importlib.import_module('itertools')
Checking if a module can be imported
------------------------------------
If you need to find out if a module can be imported without actually
doing the import, then you should use "importlib.util.find_spec()".
import importlib.util
import sys
# For illustrative purposes.
name = 'itertools'
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
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
Setting up an importer
----------------------
For deep customizations of import, you typically want to implement an
*importer*. This means managing both the *finder* and *loader* side of
things. For finders there are two flavours to choose from depending on
your needs: a *meta path finder* or a *path entry finder*. The former
is what you would put on "sys.meta_path" while the latter is what you
create using a *path entry hook* on "sys.path_hooks" which works with
"sys.path" entries to potentially create a finder. This example will
show you how to register your own importers so that import will use
them (for creating an importer for yourself, read the documentation
for the appropriate classes defined within this package):
import importlib.machinery
import sys
# For illustrative purposes only.
SpamMetaPathFinder = importlib.machinery.PathFinder
SpamPathEntryFinder = importlib.machinery.FileFinder
loader_details = (importlib.machinery.SourceFileLoader,
importlib.machinery.SOURCE_SUFFIXES)
# Setting up a meta path finder.
# Make sure to put the finder in the proper location in the list in terms of
# priority.
sys.meta_path.append(SpamMetaPathFinder)
# Setting up a path entry finder.
# Make sure to put the path hook in the proper location in the list in terms
# of priority.
sys.path_hooks.append(SpamPathEntryFinder.path_hook(loader_details))
Approximating "importlib.import_module()"
-----------------------------------------
Import itself is implemented in Python code, making it possible to
expose most of the import machinery through importlib. The following
helps illustrate the various APIs that importlib exposes by providing
an approximate implementation of "importlib.import_module()" (Python
3.4 and newer for the importlib usage, Python 3.6 and newer for other
parts of the code).
import importlib.util
import sys
def import_module(name, package=None):
"""An approximate implementation of import."""
absolute_name = importlib.util.resolve_name(name, package)
try:
return sys.modules[absolute_name]
except KeyError:
pass
path = None
if '.' in absolute_name:
parent_name, _, child_name = absolute_name.rpartition('.')
parent_module = import_module(parent_name)
path = parent_module.spec.submodule_search_locations
for finder in sys.meta_path:
spec = finder.find_spec(absolute_name, path)
if spec is not None:
break
else:
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
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