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Rename proposed files from .pkg into .pth. Drop 

claims that this extends the .pkg mechanism.
This commit is contained in:
Martin v. Löwis 2009-04-30 09:05:00 +00:00
parent d0df1270f4
commit 35daf4cb35
1 changed files with 20 additions and 25 deletions
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pep-0382.txt
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@ -49,8 +49,8 @@ invoked independent of which portion of the package gets imported
first. As a consequence, the package's ``__init__.py`` cannot first. As a consequence, the package's ``__init__.py`` cannot
practically define any names as it depends on the order of the package practically define any names as it depends on the order of the package
fragments on sys.path which portion is imported first. As a special fragments on sys.path which portion is imported first. As a special
feature, extend_path reads files named ``*.pkg`` which allow to feature, extend_path reads files named ``<packagename>.pkg`` which
declare additional portions. allow to declare additional portions.
setuptools provides a similar function pkg_resources.declare_namespace setuptools provides a similar function pkg_resources.declare_namespace
that is used in the form:: that is used in the form::
@ -91,29 +91,27 @@ Specification
Rather than using an imperative mechanism for importing packages, a Rather than using an imperative mechanism for importing packages, a
declarative approach is proposed here, as an extension to the existing declarative approach is proposed here, as an extension to the existing
``*.pkg`` mechanism. ``*.pth`` mechanism available on the top-level python path.
The import statement is extended so that it directly considers ``*.pkg`` The import statement is extended so that it directly considers
files during import; a directory is considered a package if it either ``*.pth`` files during import; a directory is considered a package if
contains a file named __init__.py, or a file whose name ends with it either contains a file named __init__.py, or a file whose name ends
".pkg". with ".pth". Unlike .pth files on the top level, lines starting with
"import" are not supported in per-package .pth files.
In addition, the format of the ``*.pkg`` file is extended: a line with In addition, the format of the ``*.pth`` file is extended: a line with
the single character ``*`` indicates that the entire sys.path will the single character ``*`` indicates that the entire sys.path will
be searched for portions of the namespace package at the time the be searched for portions of the namespace package at the time the
namespace packages is imported. namespace packages is imported.
Importing a package will immediately compute the package's __path__; Importing a package will immediately compute the package's __path__;
the ``*.pkg`` files are not considered anymore after the initial import. the ``*.pth`` files are not considered anymore after the initial
If a ``*.pkg`` package contains an asterisk, this asterisk is prepended import. If a ``*.pth`` package contains an asterisk, this asterisk is
to the package's __path__ to indicate that the package is a namespace prepended to the package's __path__ to indicate that the package is a
package (and that thus further extensions to sys.path might also namespace package (and that thus further extensions to sys.path might
want to extend __path__). At most one such asterisk gets prepended also want to extend __path__). At most one such asterisk gets
to the path. In addition, the (possibly dotted) names of all namespace prepended to the path. In addition, the (possibly dotted) names of all
packages are added to the set sys.namespace_packages. namespace packages are added to the set sys.namespace_packages.
extend_path will be extended to recognize namespace packages according
to this PEP, and avoid adding directories twice to __path__.
No other change to the importing mechanism is made; searching modules No other change to the importing mechanism is made; searching modules
(including __init__.py) will continue to stop at the first module (including __init__.py) will continue to stop at the first module
@ -122,22 +120,22 @@ this:
1. sys.path is search for a directory foo, or a file foo.<ext>. 1. sys.path is search for a directory foo, or a file foo.<ext>.
If a file is found, it is treated as a module, and imported. If a file is found, it is treated as a module, and imported.
2. if it is a directory, it checks for \*.pkg files. If it finds 2. if it is a directory, it checks for \*.pth files. If it finds
any, a package is created, and its __path__ is extended. any, a package is created, and its __path__ is extended.
3. The __init__ module is imported; this import will search the 3. The __init__ module is imported; this import will search the
__path__ that got computed already. __path__ that got computed already.
4. If neither a \*.pkg file nor an __init__.py was found, the 4. If neither a \*.pth file nor an __init__.py was found, the
directory is skipped, and search for the module/package directory is skipped, and search for the module/package
continues. continues.
Discussion Discussion
========== ==========
With the addition of ``*.pkg`` files to the import mechanism, namespace With the addition of ``*.pth`` files to the import mechanism, namespace
packages can stop filling out the namespace package's __init__.py. packages can stop filling out the namespace package's __init__.py.
As a consequence, extend_path and declare_namespace become obsolete. As a consequence, extend_path and declare_namespace become obsolete.
It is recommended that distributions put a file <distribution>.pkg It is recommended that distributions put a file <distribution>.pth
into their namespace packages, with a single asterisk. This allows into their namespace packages, with a single asterisk. This allows
vendor packages to install multiple portions of namespace package vendor packages to install multiple portions of namespace package
into a single directory, with no risk of overlapping files. into a single directory, with no risk of overlapping files.
@ -160,9 +158,6 @@ having users and tools starting to special-case 2.7). Prospective
users of this feature are encouraged to comment on this particular users of this feature are encouraged to comment on this particular
question. question.
It also has been proposed to rename the extension from .pkg to
something else.
Copyright Copyright
========= =========