mirror of https://github.com/python/cpython
517 lines
20 KiB
ReStructuredText
517 lines
20 KiB
ReStructuredText
:mod:`importlib` -- An implementation of :keyword:`import`
|
|
==========================================================
|
|
|
|
.. module:: importlib
|
|
:synopsis: An implementation of the import machinery.
|
|
|
|
.. moduleauthor:: Brett Cannon <brett@python.org>
|
|
.. sectionauthor:: Brett Cannon <brett@python.org>
|
|
|
|
.. versionadded:: 3.1
|
|
|
|
|
|
Introduction
|
|
------------
|
|
|
|
The purpose of the :mod:`importlib` package is two-fold. One is to provide an
|
|
implementation of the :keyword:`import` statement (and thus, by extension, the
|
|
:func:`__import__` function) in Python source code. This provides an
|
|
implementation of :keyword:`import` which is portable to any Python
|
|
interpreter. This also provides a reference implementation which is easier to
|
|
comprehend than one in a programming language other than Python.
|
|
|
|
Two, the components to implement :keyword:`import` can be exposed in this
|
|
package, making it easier for users to create their own custom objects (known
|
|
generically as an :term:`importer`) to participate in the import process.
|
|
Details on providing custom importers can be found in :pep:`302`.
|
|
|
|
.. seealso::
|
|
|
|
:ref:`import`
|
|
The language reference for the :keyword:`import` statement.
|
|
|
|
`Packages specification <http://www.python.org/doc/essays/packages.html>`__
|
|
Original specification of packages. Some semantics have changed since
|
|
the writing of this document (e.g. redirecting based on :keyword:`None`
|
|
in :data:`sys.modules`).
|
|
|
|
The :func:`.__import__` function
|
|
The built-in function for which the :keyword:`import` statement is
|
|
syntactic sugar.
|
|
|
|
: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:`3128`
|
|
Using UTF-8 as the Default Source Encoding
|
|
|
|
|
|
Functions
|
|
---------
|
|
|
|
.. function:: __import__(name, globals={}, locals={}, fromlist=list(), level=0)
|
|
|
|
An implementation of the built-in :func:`__import__` function. See the
|
|
built-in function's documentation for usage instructions.
|
|
|
|
.. function:: import_module(name, package=None)
|
|
|
|
Import a module. The *name* argument specifies what module to
|
|
import in absolute or relative terms
|
|
(e.g. either ``pkg.mod`` or ``..mod``). If the name is
|
|
specified in relative terms, then the *package* argument must be set to
|
|
the name of the package which is to act as the anchor for resolving the
|
|
package name (e.g. ``import_module('..mod', 'pkg.subpkg')`` will import
|
|
``pkg.mod``).
|
|
|
|
The :func:`import_module` function acts as a simplifying wrapper around
|
|
:func:`importlib.__import__`. This means all semantics of the function are
|
|
derived from :func:`importlib.__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 that :func:`import_module` returns the most nested package or module
|
|
that was imported (e.g. ``pkg.mod``), while :func:`__import__` returns the
|
|
top-level package or module (e.g. ``pkg``).
|
|
|
|
|
|
:mod:`importlib.abc` -- Abstract base classes related to import
|
|
---------------------------------------------------------------
|
|
|
|
.. module:: importlib.abc
|
|
:synopsis: Abstract base classes related to import
|
|
|
|
The :mod:`importlib.abc` module contains all of the core abstract base classes
|
|
used by :keyword:`import`. Some subclasses of the core abstract base classes
|
|
are also provided to help in implementing the core ABCs.
|
|
|
|
|
|
.. class:: Finder
|
|
|
|
An abstract base class representing a :term:`finder`.
|
|
See :pep:`302` for the exact definition for a finder.
|
|
|
|
.. method:: find_module(fullname, path=None)
|
|
|
|
An abstract method for finding a :term:`loader` for the specified
|
|
module. If the :term:`finder` is found on :data:`sys.meta_path` and the
|
|
module to be searched for is a subpackage or module then *path* will
|
|
be the value of :attr:`__path__` from the parent package. If a loader
|
|
cannot be found, :keyword:`None` is returned.
|
|
|
|
|
|
.. class:: Loader
|
|
|
|
An abstract base class for a :term:`loader`.
|
|
See :pep:`302` for the exact definition for a loader.
|
|
|
|
.. method:: load_module(fullname)
|
|
|
|
An abstract method for loading a module. If the module cannot be
|
|
loaded, :exc:`ImportError` is raised, otherwise the loaded module is
|
|
returned.
|
|
|
|
If the requested module already exists in :data:`sys.modules`, that
|
|
module should be used and reloaded.
|
|
Otherwise the loader should create a new module and insert it into
|
|
:data:`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 :data:`sys.modules`; modules already
|
|
in :data:`sys.modules` before the loader began execution should be left
|
|
alone. The :func:`importlib.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.)
|
|
|
|
- :attr:`__name__`
|
|
The name of the module.
|
|
|
|
- :attr:`__file__`
|
|
The path to where the module data is stored (not set for built-in
|
|
modules).
|
|
|
|
- :attr:`__path__`
|
|
A list of strings specifying the search path within a
|
|
package. This attribute is not set on modules.
|
|
|
|
- :attr:`__package__`
|
|
The parent package for the module/package. If the module is
|
|
top-level then it has a value of the empty string. The
|
|
:func:`importlib.util.set_package` decorator can handle the details
|
|
for :attr:`__package__`.
|
|
|
|
- :attr:`__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 :term:`loader` is used.)
|
|
|
|
|
|
.. class:: ResourceLoader
|
|
|
|
An abstract base class for a :term:`loader` which implements the optional
|
|
:pep:`302` protocol for loading arbitrary resources from the storage
|
|
back-end.
|
|
|
|
.. method:: 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. :exc:`IOError` is to be raised if the *path* cannot
|
|
be found. The *path* is expected to be constructed using a module's
|
|
:attr:`__file__` attribute or an item from a package's :attr:`__path__`.
|
|
|
|
|
|
.. class:: InspectLoader
|
|
|
|
An abstract base class for a :term:`loader` which implements the optional
|
|
:pep:`302` protocol for loaders that inspect modules.
|
|
|
|
.. method:: get_code(fullname)
|
|
|
|
An abstract method to return the :class:`code` object for a module.
|
|
:keyword:`None` is returned if the module does not have a code object
|
|
(e.g. built-in module). :exc:`ImportError` is raised if loader cannot
|
|
find the requested module.
|
|
|
|
.. method:: get_source(fullname)
|
|
|
|
An abstract method to return the source of a module. It is returned as
|
|
a text string with universal newlines. Returns :keyword:`None` if no
|
|
source is available (e.g. a built-in module). Raises :exc:`ImportError`
|
|
if the loader cannot find the module specified.
|
|
|
|
.. method:: is_package(fullname)
|
|
|
|
An abstract method to return a true value if the module is a package, a
|
|
false value otherwise. :exc:`ImportError` is raised if the
|
|
:term:`loader` cannot find the module.
|
|
|
|
|
|
.. class:: ExecutionLoader
|
|
|
|
An abstract base class which inherits from :class:`InspectLoader` that,
|
|
when implemented, helps a module to be executed as a script. The ABC
|
|
represents an optional :pep:`302` protocol.
|
|
|
|
.. method:: get_filename(fullname)
|
|
|
|
An abstract method that is to return the value for :attr:`__file__` for
|
|
the specified module. If no path is available, :exc:`ImportError` is
|
|
raised.
|
|
|
|
|
|
.. class:: PyLoader
|
|
|
|
An abstract base class inheriting from
|
|
:class:`importlib.abc.ExecutionLoader` and
|
|
:class:`importlib.abc.ResourceLoader` designed to ease the loading of
|
|
Python source modules (bytecode is not handled; see
|
|
:class:`importlib.abc.PyPycLoader` 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.
|
|
|
|
.. method:: source_path(fullname)
|
|
|
|
An abstract method that returns the path to the source code for a
|
|
module. Should return :keyword:`None` if there is no source code.
|
|
Raises :exc:`ImportError` if the loader knows it cannot handle the
|
|
module.
|
|
|
|
.. method:: get_filename(fullname)
|
|
|
|
A concrete implementation of
|
|
:meth:`importlib.abc.ExecutionLoader.get_filename` that
|
|
relies on :meth:`source_path`. If :meth:`source_path` returns
|
|
:keyword:`None`, then :exc:`ImportError` is raised.
|
|
|
|
.. method:: load_module(fullname)
|
|
|
|
A concrete implementation of :meth:`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
|
|
:attr:`__path__` is set to ``[os.path.dirname(__file__)]``.
|
|
|
|
.. method:: get_code(fullname)
|
|
|
|
A concrete implementation of
|
|
:meth:`importlib.abc.InspectLoader.get_code` that creates code objects
|
|
from Python source code, by requesting the source code (using
|
|
:meth:`source_path` and :meth:`get_data`) and compiling it with the
|
|
built-in :func:`compile` function.
|
|
|
|
.. method:: get_source(fullname)
|
|
|
|
A concrete implementation of
|
|
:meth:`importlib.abc.InspectLoader.get_source`. Uses
|
|
:meth:`importlib.abc.ResourceLoader.get_data` and :meth:`source_path`
|
|
to get the source code. It tries to guess the source encoding using
|
|
:func:`tokenize.detect_encoding`.
|
|
|
|
|
|
.. class:: PyPycLoader
|
|
|
|
An abstract base class inheriting from :class:`importlib.abc.PyLoader`.
|
|
This ABC is meant to help in creating loaders that support both Python
|
|
source and bytecode.
|
|
|
|
.. method:: 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 :keyword:`None`. If the
|
|
module cannot be found then :exc:`ImportError` is raised.
|
|
|
|
.. method:: bytecode_path(fullname)
|
|
|
|
An abstract method which returns the path to the bytecode for the
|
|
specified module, if it exists. It returns :keyword:`None`
|
|
if no bytecode exists (yet).
|
|
Raises :exc:`ImportError` if the loader knows it cannot handle the
|
|
module.
|
|
|
|
.. method:: get_filename(fullname)
|
|
|
|
A concrete implementation of
|
|
:meth:`importlib.abc.ExecutionLoader.get_filename` that relies on
|
|
:meth:`importlib.abc.PyLoader.source_path` and :meth:`bytecode_path`.
|
|
If :meth:`source_path` returns a path, then that value is returned.
|
|
Else if :meth:`bytecode_path` returns a path, that path will be
|
|
returned. If a path is not available from both methods,
|
|
:exc:`ImportError` is raised.
|
|
|
|
.. method:: write_bytecode(fullname, bytecode)
|
|
|
|
An abstract method which has the loader write *bytecode* for future
|
|
use. If the bytecode is written, return :keyword:`True`. Return
|
|
:keyword:`False` if the bytecode could not be written. This method
|
|
should not be called if :data:`sys.dont_write_bytecode` is true.
|
|
The *bytecode* argument should be a bytes string or bytes array.
|
|
|
|
|
|
:mod:`importlib.machinery` -- Importers and path hooks
|
|
------------------------------------------------------
|
|
|
|
.. module:: importlib.machinery
|
|
:synopsis: Importers and path hooks
|
|
|
|
This module contains the various objects that help :keyword:`import`
|
|
find and load modules.
|
|
|
|
.. class:: BuiltinImporter
|
|
|
|
An :term:`importer` for built-in modules. All known built-in modules are
|
|
listed in :data:`sys.builtin_module_names`. This class implements the
|
|
:class:`importlib.abc.Finder` and :class:`importlib.abc.InspectLoader`
|
|
ABCs.
|
|
|
|
Only class methods are defined by this class to alleviate the need for
|
|
instantiation.
|
|
|
|
|
|
.. class:: FrozenImporter
|
|
|
|
An :term:`importer` for frozen modules. This class implements the
|
|
:class:`importlib.abc.Finder` and :class:`importlib.abc.InspectLoader`
|
|
ABCs.
|
|
|
|
Only class methods are defined by this class to alleviate the need for
|
|
instantiation.
|
|
|
|
|
|
.. class:: PathFinder
|
|
|
|
:term:`Finder` for :data:`sys.path`. This class implements the
|
|
:class:`importlib.abc.Finder` ABC.
|
|
|
|
This class does not perfectly mirror the semantics of :keyword:`import` in
|
|
terms of :data:`sys.path`. No implicit path hooks are assumed for
|
|
simplification of the class and its semantics.
|
|
|
|
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 :term:`loader` for the module
|
|
specified by *fullname* on :data:`sys.path` or, if defined, on
|
|
*path*. For each path entry that is searched,
|
|
:data:`sys.path_importer_cache` is checked. If an non-false object is
|
|
found then it is used as the :term:`finder` to look for the module
|
|
being searched for. If no entry is found in
|
|
:data:`sys.path_importer_cache`, then :data:`sys.path_hooks` is
|
|
searched for a finder for the path entry and, if found, is stored in
|
|
:data:`sys.path_importer_cache` along with being queried about the
|
|
module. If no finder is ever found then :keyword:`None` is returned.
|
|
|
|
|
|
:mod:`importlib.util` -- Utility code for importers
|
|
---------------------------------------------------
|
|
|
|
.. module:: importlib.util
|
|
:synopsis: Importers and path hooks
|
|
|
|
This module contains the various objects that help in the construction of
|
|
an :term:`importer`.
|
|
|
|
.. function:: module_for_loader(method)
|
|
|
|
A :term:`decorator` for a :term:`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 :term:`loader`. If the module is not found in
|
|
:data:`sys.modules` then a new one is constructed with its
|
|
:attr:`__name__` attribute set. Otherwise the module found in
|
|
:data:`sys.modules` will be passed into the method. If an
|
|
exception is raised by the decorated method and a module was added to
|
|
:data:`sys.modules` it will be removed to prevent a partially initialized
|
|
module from being in left in :data:`sys.modules`. If the module was already
|
|
in :data:`sys.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`.
|
|
|
|
.. function:: set_loader(fxn)
|
|
|
|
A :term:`decorator` for a :term:`loader` method,
|
|
to set the :attr:`__loader__`
|
|
attribute on loaded modules. If the attribute is already set the decorator
|
|
does nothing. It is assumed that the first positional argument to the
|
|
wrapped method is what :attr:`__loader__` should be set to.
|
|
|
|
.. function:: set_package(fxn)
|
|
|
|
A :term:`decorator` for a :term:`loader` to set the :attr:`__package__`
|
|
attribute on the module returned by the loader. If :attr:`__package__` is
|
|
set and has a value other than :keyword:`None` 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 in :data:`sys.modules`.
|
|
|
|
Reliance on this decorator is discouraged when it is possible to set
|
|
:attr:`__package__` before the execution of the code is possible. By
|
|
setting it before the code for the module is executed it allows the
|
|
attribute to be used at the global level of the module during
|
|
initialization.
|
|
|
|
|
|
Example
|
|
-------
|
|
|
|
Below is an example meta path importer that uses a dict for back-end storage
|
|
for source code. While not an optimal solution -- manipulations of
|
|
:attr:`__path__` on packages does not influence import -- it does illustrate
|
|
what little is required to implement an importer.
|
|
|
|
.. testcode::
|
|
|
|
"""An importer where source is stored in a dict."""
|
|
from importlib import abc
|
|
|
|
|
|
class DictImporter(abc.Finder, abc.PyLoader):
|
|
|
|
"""A meta path importer that stores source code in a dict.
|
|
|
|
The keys are the module names -- packages must end in ``.__init__``.
|
|
The values must be something that can be passed to 'bytes'.
|
|
|
|
"""
|
|
|
|
def __init__(self, memory):
|
|
"""Store the dict."""
|
|
self.memory = memory
|
|
|
|
def contains(self, name):
|
|
"""See if a module or package is in the dict."""
|
|
if name in self.memory:
|
|
return name
|
|
package_name = '{}.__init__'.format(name)
|
|
if package_name in self.memory:
|
|
return package_name
|
|
return False
|
|
|
|
__contains__ = contains # Convenience.
|
|
|
|
def find_module(self, fullname, path=None):
|
|
"""Find the module in the dict."""
|
|
if fullname in self:
|
|
return self
|
|
return None
|
|
|
|
def source_path(self, fullname):
|
|
"""Return the module name if the module is in the dict."""
|
|
if not fullname in self:
|
|
raise ImportError
|
|
return fullname
|
|
|
|
def get_data(self, path):
|
|
"""Return the bytes for the source.
|
|
|
|
The value found in the dict is passed through 'bytes' before being
|
|
returned.
|
|
|
|
"""
|
|
name = self.contains(path)
|
|
if not name:
|
|
raise IOError
|
|
return bytes(self.memory[name])
|
|
|
|
def is_package(self, fullname):
|
|
"""Tell if module is a package based on whether the dict contains the
|
|
name with ``.__init__`` appended to it."""
|
|
if fullname not in self:
|
|
raise ImportError
|
|
if fullname in self.memory:
|
|
return False
|
|
# If name is in this importer but not as it is then it must end in
|
|
# ``__init__``.
|
|
else:
|
|
return True
|
|
|
|
.. testcode::
|
|
:hide:
|
|
|
|
import importlib
|
|
import sys
|
|
|
|
|
|
# Build the dict; keys of name, value of __package__.
|
|
names = {'_top_level': '', '_pkg.__init__': '_pkg', '_pkg.mod': '_pkg'}
|
|
source = {name: "name = {!r}".format(name).encode() for name in names}
|
|
|
|
# Register the meta path importer.
|
|
importer = DictImporter(source)
|
|
sys.meta_path.append(importer)
|
|
|
|
# Sanity check.
|
|
for name in names:
|
|
module = importlib.import_module(name)
|
|
assert module.__name__ == name
|
|
assert getattr(module, 'name') == name
|
|
assert module.__loader__ is importer
|
|
assert module.__package__ == names[name]
|