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61b14251d3
This required moving the class from importlib/abc.py into importlib/_bootstrap.py and jiggering some code to work better with the class. This included changing how the file finder worked to better meet import semantics. This also led to fixing importlib to handle the empty string from sys.path as import currently does (and making me wish we didn't support that instead just required people to insert '.' instead to represent cwd). It also required making the new set_data abstractmethod create any needed subdirectories implicitly thanks to __pycache__ (it was either this or grow the SourceLoader ABC to gain an 'exists' method and either a mkdir method or have set_data with no data arg mean to create a directory). Lastly, as an optimization the file loaders cache the file path where the finder found something to use for loading (this is thanks to having a sourceless loader separate from the source loader to simplify the code and cut out stat calls). Unfortunately test_runpy assumed a loader would always work for a module, even if you changed from underneath it what it was expected to work with. By simply dropping the previous loader in test_runpy so the proper loader can be returned by the finder fixed the failure. At this point importlib deviates from import on two points: 1. The exception raised when trying to import a file is different (import does an explicit file check to print a special message, importlib just says the path cannot be imported as if it was just some module name). 2. the co_filename on a code object is not being set to where bytecode was actually loaded from instead of where the marshalled code object originally came from (a solution for this has already been agreed upon on python-dev but has not been implemented yet; issue8611).
518 lines
20 KiB
ReStructuredText
518 lines
20 KiB
ReStructuredText
:mod:`importlib` -- An implementation of :keyword:`import`
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==========================================================
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.. module:: importlib
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:synopsis: An implementation of the import machinery.
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.. moduleauthor:: Brett Cannon <brett@python.org>
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.. sectionauthor:: Brett Cannon <brett@python.org>
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.. versionadded:: 3.1
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Introduction
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------------
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The purpose of the :mod:`importlib` package is two-fold. One is to provide an
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implementation of the :keyword:`import` statement (and thus, by extension, the
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:func:`__import__` function) in Python source code. This provides an
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implementation of :keyword:`import` which is portable to any Python
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interpreter. This also provides a reference implementation which is easier to
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comprehend than one implemented in a programming language other than Python.
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Two, the components to implement :keyword:`import` are exposed in this
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package, making it easier for users to create their own custom objects (known
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generically as an :term:`importer`) to participate in the import process.
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Details on custom importers can be found in :pep:`302`.
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.. seealso::
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:ref:`import`
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The language reference for the :keyword:`import` statement.
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`Packages specification <http://www.python.org/doc/essays/packages.html>`__
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Original specification of packages. Some semantics have changed since
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the writing of this document (e.g. redirecting based on :keyword:`None`
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in :data:`sys.modules`).
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The :func:`.__import__` function
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The :keyword:`import` statement is syntactic sugar for this function.
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:pep:`235`
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Import on Case-Insensitive Platforms
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:pep:`263`
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Defining Python Source Code Encodings
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:pep:`302`
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New Import Hooks
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:pep:`328`
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Imports: Multi-Line and Absolute/Relative
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:pep:`366`
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Main module explicit relative imports
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:pep:`3120`
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Using UTF-8 as the Default Source Encoding
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:pep:`3147`
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PYC Repository Directories
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Functions
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---------
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.. function:: __import__(name, globals={}, locals={}, fromlist=list(), level=0)
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An implementation of the built-in :func:`__import__` function.
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.. function:: import_module(name, package=None)
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Import a module. The *name* argument specifies what module to
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import in absolute or relative terms
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(e.g. either ``pkg.mod`` or ``..mod``). If the name is
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specified in relative terms, then the *package* argument must be set to
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the name of the package which is to act as the anchor for resolving the
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package name (e.g. ``import_module('..mod', 'pkg.subpkg')`` will import
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``pkg.mod``).
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The :func:`import_module` function acts as a simplifying wrapper around
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:func:`importlib.__import__`. This means all semantics of the function are
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derived from :func:`importlib.__import__`, including requiring the package
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from which an import is occurring to have been previously imported
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(i.e., *package* must already be imported). The most important difference
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is that :func:`import_module` returns the most nested package or module
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that was imported (e.g. ``pkg.mod``), while :func:`__import__` returns the
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top-level package or module (e.g. ``pkg``).
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:mod:`importlib.abc` -- Abstract base classes related to import
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---------------------------------------------------------------
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.. module:: importlib.abc
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:synopsis: Abstract base classes related to import
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The :mod:`importlib.abc` module contains all of the core abstract base classes
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used by :keyword:`import`. Some subclasses of the core abstract base classes
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are also provided to help in implementing the core ABCs.
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.. class:: Finder
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An abstract base class representing a :term:`finder`.
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See :pep:`302` for the exact definition for a finder.
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.. method:: find_module(fullname, path=None)
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An abstract method for finding a :term:`loader` for the specified
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module. If the :term:`finder` is found on :data:`sys.meta_path` and the
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module to be searched for is a subpackage or module then *path* will
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be the value of :attr:`__path__` from the parent package. If a loader
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cannot be found, :keyword:`None` is returned.
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.. class:: Loader
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An abstract base class for a :term:`loader`.
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See :pep:`302` for the exact definition for a loader.
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.. method:: load_module(fullname)
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An abstract method for loading a module. If the module cannot be
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loaded, :exc:`ImportError` is raised, otherwise the loaded module is
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returned.
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If the requested module already exists in :data:`sys.modules`, that
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module should be used and reloaded.
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Otherwise the loader should create a new module and insert it into
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:data:`sys.modules` before any loading begins, to prevent recursion
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from the import. If the loader inserted a module and the load fails, it
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must be removed by the loader from :data:`sys.modules`; modules already
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in :data:`sys.modules` before the loader began execution should be left
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alone. The :func:`importlib.util.module_for_loader` decorator handles
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all of these details.
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The loader should set several attributes on the module.
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(Note that some of these attributes can change when a module is
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reloaded.)
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- :attr:`__name__`
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The name of the module.
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- :attr:`__file__`
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The path to where the module data is stored (not set for built-in
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modules).
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- :attr:`__path__`
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A list of strings specifying the search path within a
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package. This attribute is not set on modules.
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- :attr:`__package__`
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The parent package for the module/package. If the module is
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top-level then it has a value of the empty string. The
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:func:`importlib.util.set_package` decorator can handle the details
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for :attr:`__package__`.
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- :attr:`__loader__`
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The loader used to load the module.
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(This is not set by the built-in import machinery,
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but it should be set whenever a :term:`loader` is used.)
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.. class:: ResourceLoader
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An abstract base class for a :term:`loader` which implements the optional
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:pep:`302` protocol for loading arbitrary resources from the storage
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back-end.
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.. method:: get_data(path)
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An abstract method to return the bytes for the data located at *path*.
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Loaders that have a file-like storage back-end
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that allows storing arbitrary data
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can implement this abstract method to give direct access
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to the data stored. :exc:`IOError` is to be raised if the *path* cannot
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be found. The *path* is expected to be constructed using a module's
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:attr:`__file__` attribute or an item from a package's :attr:`__path__`.
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.. class:: InspectLoader
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An abstract base class for a :term:`loader` which implements the optional
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:pep:`302` protocol for loaders that inspect modules.
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.. method:: get_code(fullname)
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An abstract method to return the :class:`code` object for a module.
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:keyword:`None` is returned if the module does not have a code object
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(e.g. built-in module). :exc:`ImportError` is raised if loader cannot
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find the requested module.
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.. method:: get_source(fullname)
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An abstract method to return the source of a module. It is returned as
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a text string with universal newlines. Returns :keyword:`None` if no
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source is available (e.g. a built-in module). Raises :exc:`ImportError`
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if the loader cannot find the module specified.
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.. method:: is_package(fullname)
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An abstract method to return a true value if the module is a package, a
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false value otherwise. :exc:`ImportError` is raised if the
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:term:`loader` cannot find the module.
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.. class:: ExecutionLoader
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An abstract base class which inherits from :class:`InspectLoader` that,
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when implemented, helps a module to be executed as a script. The ABC
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represents an optional :pep:`302` protocol.
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.. method:: get_filename(fullname)
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An abstract method that is to return the value of :attr:`__file__` for
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the specified module. If no path is available, :exc:`ImportError` is
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raised.
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If source code is available, then the method should return the path to
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the source file, regardless of whether a bytecode was used to load the
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module.
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.. class:: SourceLoader
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An abstract base class for implementing source (and optionally bytecode)
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file loading. The class inherits from both :class:`ResourceLoader` and
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:class:`ExecutionLoader`, requiring the implementation of:
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* :meth:`ResourceLoader.get_data`
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* :meth:`ExecutionLoader.get_filename`
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Implement to only return the path to the source file; sourceless
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loading is not supported.
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The abstract methods defined by this class are to add optional bytecode
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file support. Not implementing these optional methods causes the loader to
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only work with source code. Implementing the methods allows the loader to
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work with source *and* bytecode files; it does not allow for *sourceless*
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loading where only bytecode is provided. Bytecode files are an
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optimization to speed up loading by removing the parsing step of Python's
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compiler, and so no bytecode-specific API is exposed.
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.. method:: path_mtime(self, path)
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Optional abstract method which returns the modification time for the
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specified path.
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.. method:: set_data(self, path, data)
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Optional abstract method which writes the specified bytes to a file
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path. Any intermediate directories which do not exist are to be created
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automatically.
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When writing to the path fails because the path is read-only
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(:attr:`errno.EACCES`), do not propagate the exception.
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.. method:: get_code(self, fullname)
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Concrete implementation of :meth:`InspectLoader.get_code`.
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.. method:: load_module(self, fullname)
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Concrete implementation of :meth:`Loader.load_module`.
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.. method:: get_source(self, fullname)
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Concrete implementation of :meth:`InspectLoader.get_source`.
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.. method:: is_package(self, fullname)
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Concrete implementation of :meth:`InspectLoader.is_package`. A module
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is determined to be a package if its file path is a file named
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``__init__`` when the file extension is removed.
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.. class:: PyLoader
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An abstract base class inheriting from
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:class:`ExecutionLoader` and
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:class:`ResourceLoader` designed to ease the loading of
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Python source modules (bytecode is not handled; see
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:class:`SourceLoader` for a source/bytecode ABC). A subclass
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implementing this ABC will only need to worry about exposing how the source
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code is stored; all other details for loading Python source code will be
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handled by the concrete implementations of key methods.
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.. deprecated:: 3.2
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This class has been deprecated in favor of :class:`SourceLoader` and is
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slated for removal in Python 3.4. See below for how to create a
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subclass that is compatbile with Python 3.1 onwards.
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If compatibility with Python 3.1 is required, then use the following idiom
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to implement a subclass that will work with Python 3.1 onwards (make sure
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to implement :meth:`ExecutionLoader.get_filename`)::
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try:
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from importlib.abc import SourceLoader
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except ImportError:
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from importlib.abc import PyLoader as SourceLoader
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class CustomLoader(SourceLoader):
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def get_filename(self, fullname):
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"""Return the path to the source file."""
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# Implement ...
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def source_path(self, fullname):
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"""Implement source_path in terms of get_filename."""
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try:
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return self.get_filename(fullname)
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except ImportError:
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return None
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def is_package(self, fullname):
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"""Implement is_package by looking for an __init__ file
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name as returned by get_filename."""
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filename = os.path.basename(self.get_filename(fullname))
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return os.path.splitext(filename)[0] == '__init__'
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.. method:: source_path(fullname)
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An abstract method that returns the path to the source code for a
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module. Should return :keyword:`None` if there is no source code.
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Raises :exc:`ImportError` if the loader knows it cannot handle the
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module.
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.. method:: get_filename(fullname)
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A concrete implementation of
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:meth:`importlib.abc.ExecutionLoader.get_filename` that
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relies on :meth:`source_path`. If :meth:`source_path` returns
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:keyword:`None`, then :exc:`ImportError` is raised.
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.. method:: load_module(fullname)
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A concrete implementation of :meth:`importlib.abc.Loader.load_module`
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that loads Python source code. All needed information comes from the
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abstract methods required by this ABC. The only pertinent assumption
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made by this method is that when loading a package
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:attr:`__path__` is set to ``[os.path.dirname(__file__)]``.
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.. method:: get_code(fullname)
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A concrete implementation of
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:meth:`importlib.abc.InspectLoader.get_code` that creates code objects
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from Python source code, by requesting the source code (using
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:meth:`source_path` and :meth:`get_data`) and compiling it with the
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built-in :func:`compile` function.
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.. method:: get_source(fullname)
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A concrete implementation of
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:meth:`importlib.abc.InspectLoader.get_source`. Uses
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:meth:`importlib.abc.ResourceLoader.get_data` and :meth:`source_path`
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to get the source code. It tries to guess the source encoding using
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:func:`tokenize.detect_encoding`.
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.. class:: PyPycLoader
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An abstract base class inheriting from :class:`PyLoader`.
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This ABC is meant to help in creating loaders that support both Python
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source and bytecode.
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.. deprecated:: 3.2
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This class has been deprecated in favor of :class:`SourceLoader` and to
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properly support :pep:`3147`. If compatibility is required with
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Python 3.1, implement both :class:`SourceLoader` and :class:`PyLoader`;
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instructions on how to do so are included in the documentation for
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:class:`PyLoader`. Do note that this solution will not support
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sourceless/bytecode-only loading; only source *and* bytecode loading.
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.. method:: source_mtime(fullname)
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An abstract method which returns the modification time for the source
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code of the specified module. The modification time should be an
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integer. If there is no source code, return :keyword:`None`. If the
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module cannot be found then :exc:`ImportError` is raised.
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.. method:: bytecode_path(fullname)
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An abstract method which returns the path to the bytecode for the
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specified module, if it exists. It returns :keyword:`None`
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if no bytecode exists (yet).
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Raises :exc:`ImportError` if the loader knows it cannot handle the
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module.
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.. method:: get_filename(fullname)
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A concrete implementation of
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:meth:`ExecutionLoader.get_filename` that relies on
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:meth:`PyLoader.source_path` and :meth:`bytecode_path`.
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If :meth:`source_path` returns a path, then that value is returned.
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Else if :meth:`bytecode_path` returns a path, that path will be
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returned. If a path is not available from both methods,
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:exc:`ImportError` is raised.
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.. method:: write_bytecode(fullname, bytecode)
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An abstract method which has the loader write *bytecode* for future
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use. If the bytecode is written, return :keyword:`True`. Return
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:keyword:`False` if the bytecode could not be written. This method
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should not be called if :data:`sys.dont_write_bytecode` is true.
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The *bytecode* argument should be a bytes string or bytes array.
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:mod:`importlib.machinery` -- Importers and path hooks
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------------------------------------------------------
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.. module:: importlib.machinery
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:synopsis: Importers and path hooks
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This module contains the various objects that help :keyword:`import`
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find and load modules.
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.. class:: BuiltinImporter
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An :term:`importer` for built-in modules. All known built-in modules are
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listed in :data:`sys.builtin_module_names`. This class implements the
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:class:`importlib.abc.Finder` and :class:`importlib.abc.InspectLoader`
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ABCs.
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Only class methods are defined by this class to alleviate the need for
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instantiation.
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.. class:: FrozenImporter
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An :term:`importer` for frozen modules. This class implements the
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:class:`importlib.abc.Finder` and :class:`importlib.abc.InspectLoader`
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ABCs.
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Only class methods are defined by this class to alleviate the need for
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instantiation.
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.. class:: PathFinder
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:term:`Finder` for :data:`sys.path`. This class implements the
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:class:`importlib.abc.Finder` ABC.
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This class does not perfectly mirror the semantics of :keyword:`import` in
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terms of :data:`sys.path`. No implicit path hooks are assumed for
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simplification of the class and its semantics.
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Only class methods are defined by this class to alleviate the need for
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instantiation.
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.. classmethod:: find_module(fullname, path=None)
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Class method that attempts to find a :term:`loader` for the module
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specified by *fullname* on :data:`sys.path` or, if defined, on
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*path*. For each path entry that is searched,
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:data:`sys.path_importer_cache` is checked. If an non-false object is
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found then it is used as the :term:`finder` to look for the module
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being searched for. If no entry is found in
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:data:`sys.path_importer_cache`, then :data:`sys.path_hooks` is
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searched for a finder for the path entry and, if found, is stored in
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:data:`sys.path_importer_cache` along with being queried about the
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module. If no finder is ever found then :keyword:`None` is returned.
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:mod:`importlib.util` -- Utility code for importers
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---------------------------------------------------
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.. module:: importlib.util
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:synopsis: Importers and path hooks
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This module contains the various objects that help in the construction of
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an :term:`importer`.
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.. function:: module_for_loader(method)
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A :term:`decorator` for a :term:`loader` method,
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to handle selecting the proper
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module object to load with. The decorated method is expected to have a call
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signature taking two positional arguments
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(e.g. ``load_module(self, module)``) for which the second argument
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will be the module **object** to be used by the loader.
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Note that the decorator
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will not work on static methods because of the assumption of two
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arguments.
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The decorated method will take in the **name** of the module to be loaded
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as expected for a :term:`loader`. If the module is not found in
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:data:`sys.modules` then a new one is constructed with its
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:attr:`__name__` attribute set. Otherwise the module found in
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:data:`sys.modules` will be passed into the method. If an
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exception is raised by the decorated method and a module was added to
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:data:`sys.modules` it will be removed to prevent a partially initialized
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module from being in left in :data:`sys.modules`. If the module was already
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in :data:`sys.modules` then it is left alone.
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Use of this decorator handles all the details of which module object a
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loader should initialize as specified by :pep:`302`.
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.. function:: set_loader(fxn)
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A :term:`decorator` for a :term:`loader` method,
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to set the :attr:`__loader__`
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attribute on loaded modules. If the attribute is already set the decorator
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does nothing. It is assumed that the first positional argument to the
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wrapped method is what :attr:`__loader__` should be set to.
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.. function:: set_package(fxn)
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A :term:`decorator` for a :term:`loader` to set the :attr:`__package__`
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attribute on the module returned by the loader. If :attr:`__package__` is
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set and has a value other than :keyword:`None` it will not be changed.
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Note that the module returned by the loader is what has the attribute
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set on and not the module found in :data:`sys.modules`.
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Reliance on this decorator is discouraged when it is possible to set
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:attr:`__package__` before the execution of the code is possible. By
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setting it before the code for the module is executed it allows the
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attribute to be used at the global level of the module during
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initialization.
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