[Python-checkins] r70751 - python/branches/py3k/Doc/library/importlib.rst
guido.van.rossum
python-checkins at python.org
Mon Mar 30 22:34:58 CEST 2009
Author: guido.van.rossum
Date: Mon Mar 30 22:34:57 2009
New Revision: 70751
Log:
Thorough review of importlib docs. Reviewed by Brett himself.
Modified:
python/branches/py3k/Doc/library/importlib.rst
Modified: python/branches/py3k/Doc/library/importlib.rst
==============================================================================
--- python/branches/py3k/Doc/library/importlib.rst (original)
+++ python/branches/py3k/Doc/library/importlib.rst Mon Mar 30 22:34:57 2009
@@ -37,7 +37,7 @@
The :func:`.__import__` function
The built-in function for which the :keyword:`import` statement is
- syntactic sugar for.
+ syntactic sugar.
:pep:`235`
Import on Case-Insensitive Platforms
@@ -71,8 +71,8 @@
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 package which is to act as the anchor for resolving the
+ 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``).
@@ -80,7 +80,11 @@
:func:`__import__`. This means all semantics of the function are derived
from :func:`__import__`, including requiring the package from which an
import is occurring to have been previously imported (i.e., *package*
- must already be imported).
+ 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
---------------------------------------------------------------
@@ -96,21 +100,21 @@
.. 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* is set
- to the value of :attr:`__path__` from the parent package. If a loader
+ 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.
- The exact definition of a :term:`finder` can be found in :pep:`302`.
-
.. class:: Loader
An abstract base class for a :term:`loader`.
+ See :pep:`302` for the exact definition for a loader.
.. method:: load_module(fullname)
@@ -118,18 +122,19 @@
loaded, :exc:`ImportError` is raised, otherwise the loaded module is
returned.
- If the requested module is already exists in :data:`sys.modules`, that
+ If the requested module already exists in :data:`sys.modules`, that
module should be used and reloaded.
- Otherwise a new module is to be created by the loader and inserted into
- :data:`sys.modules` before any loading begins to prevent recursion from
- the import. If the loader inserted into a module and the load fails it
+ 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 is expected to set several attributes on the module when
- adding a new module to :data:`sys.modules`.
+ 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.
@@ -139,7 +144,7 @@
modules).
- :attr:`__path__`
- Set to a list of strings specifying the search path within a
+ A list of strings specifying the search path within a
package. This attribute is not set on modules.
- :attr:`__package__`
@@ -149,9 +154,9 @@
for :attr:`__package__`.
- :attr:`__loader__`
- Set to the loader used to load the module.
-
- See :pep:`302` for the exact definition for a 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
@@ -163,17 +168,20 @@
.. 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 can implement this
- abstract method to give direct access
+ Loaders that have a file-like storage back-end
+ that allows storing arbitrary data (e.g. a zip archive loader)
+ 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:`__path__` attribute or an item from :attr:`__path__`.
+.. XXX What's the difference between the latter two? (Maybe one is __file__?)
+.. XXX Could use a clarification so as not to depend on PEP 302.
.. class:: InspectLoader
An abstract base class for a :term:`loader` which implements the optional
- :pep:`302` protocol for loaders which inspect modules.
+ :pep:`302` protocol for loaders that inspect modules.
.. method:: get_code(fullname)
@@ -185,7 +193,7 @@
.. method:: get_source(fullname)
An abstract method to return the source of a module. It is returned as
- a string with universal newline support. Returns :keyword:`None` if no
+ 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.
@@ -224,14 +232,17 @@
A concrete implementation of
:meth:`importlib.abc.InspectLoader.get_code` that creates code objects
- from Python source code.
+ from Python source code, by requesting the source code (using
+ :meth:`source_path` and :meth:`get_data`), converting it to standard
+ newlines, 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.InspectLoader.get_data` and :meth:`source_path` to
- get the source code.
+ get the source code. It tries to guess the source encoding using
+ :func:`tokenize.detect_encoding`.
.. class:: PyPycLoader
@@ -250,8 +261,9 @@
.. method:: bytecode_path(fullname)
An abstract method which returns the path to the bytecode for the
- specified module. :keyword:`None` is returned if there is no bytecode.
- :exc:`ImportError` is raised if the module is not found.
+ specified module, if it exists. It returns :keyword:`None`
+ if no bytecode exists (yet).
+ Raises :exc:`ImportError` if the module is not found.
.. method:: write_bytecode(fullname, bytecode)
@@ -259,6 +271,7 @@
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
@@ -328,16 +341,18 @@
.. function:: module_for_loader(method)
- A :term:`decorator` for a :term:`loader` which handles selecting the proper
+ 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 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
+ 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
@@ -346,18 +361,17 @@
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 what module object a
+ 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` to set the :attr:`__loader__`
+ 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__`
@@ -365,3 +379,5 @@
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`.
+
+.. XXX This whole chapter desperately needs examples...
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