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5
pep-0409.txt
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@ -8,6 +8,7 @@ Type: Standards Track
Content-Type: text/x-rst
Created: 26-Jan-2012
Post-History: 30-Aug-2002, 01-Feb-2012, 03-Feb-2012
Superseded-By: 415
Resolution: http://mail.python.org/pipermail/python-dev/2012-February/116136.html
@ -87,6 +88,10 @@ by the default exception printing routines.
Implementation Discussion
=========================
Note: after acceptance of this PEP, a cleaner implementation mechanism
was proposed and accepted in PEP 415. Refer to that PEP for more
details on the implementation actually used in Python 3.3.
Currently, ``None`` is the default for both ``__context__`` and ``__cause__``.
In order to support ``raise ... from None`` (which would set ``__cause__`` to
``None``) we need a different default value for ``__cause__``. Several ideas

26
pep-0415.txt
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@ -1,24 +1,35 @@
PEP: 415
Title: Implementing PEP 409 differently
Title: Implement context suppression with exception attributes
Version: $Revision$
Last-Modified: $Date$
Author: Benjamin Peterson <benjamin@python.org>
BDFL-Delegate: Nick Coghlan
Status: Draft
Status: Final
Type: Standards Track
Content-Type: text/x-rst
Created: 26-Feb-2012
Python-Version: 3.3
Post-History: 26-Feb-2012
Replaces: 409
Resolution: http://mail.python.org/pipermail/python-dev/2012-May/119467.html
Abstract
========
PEP 409 allows PEP 3134 exception contexts and causes to be suppressed when the
exception is printed. This is done using the ``raise exc from None``
syntax. This PEP proposes to implement context and cause suppression
differently.
PEP 409 introduced support for the ``raise exc from None`` construct to
allow the display of the exception context to be explicitly suppressed.
This PEP retains the language level changes already implemented in PEP 409,
but replaces the underlying implementation mechanism with a simpler approach
based on a new ``__suppress_context__`` attribute on all ``BaseException``
instances.
PEP Acceptance
==============
This PEP was accepted by Nick Coghlan on the 14th of May, 2012.
Rationale
=========
@ -40,6 +51,7 @@ exceptions, so it's not clear to someone inspecting an exception object why
``__cause__`` should be set to ``Ellipsis``. Using ``Ellipsis`` by default for
``__cause__`` makes it asymmetrical with ``__context__``.
Proposal
========
@ -62,6 +74,7 @@ To summarize, ``raise exc from cause`` will be equivalent to::
where ``exc.__cause__ = cause`` implicitly sets
``exc.__suppress_context__``.
Patches
=======
@ -74,6 +87,7 @@ References
.. _issue 14133:
http://bugs.python.org/issue14133
Copyright
=========

170
pep-0420.txt
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@ -34,10 +34,12 @@ Within this PEP:
* "vendor package" refers to groups of files installed by an
operating system's packaging mechanism (e.g. Debian or Redhat
packages install on Linux systems).
* "portion" refers to a set of files in a single directory (possibly
stored in a zip file) that contribute to a namespace package.
* "regular package" refers to packages as they are implemented in
Python 3.2 and earlier.
* "portion" refers to a set of files in a single directory (possibly
stored in a zip file) that contribute to a namespace package.
* "legacy portion" refers to a portion that uses ``__path__``
manipulation in order to implement namespace packages.
This PEP defines a new type of package, the "namespace package".
@ -76,6 +78,10 @@ setuptools allows declaring namespace packages in a distribution's
``setup.py``, so that distribution developers don't need to put the
magic ``__path__`` modification into ``__init__.py`` themselves.
See PEP 402's "The Problem" section [2]_ for more details on the
motivation for namespace packages. Note that PEP 402 has been
rejected, but the motivating use cases are still valid.
Rationale
=========
@ -135,48 +141,115 @@ If the scan completes without returning a module or package, and at
least one directory was recorded, then a namespace package is created.
The new namespace package:
* Has a ``__path__`` attribute set to the list of directories that
were found and recorded during the scan.
* Has a ``__path__`` attribute set to an iterable of the path strings
that were found and recorded during the scan.
* Does not have a ``__file__`` attribute.
There is no mechanism to automatically recompute the ``__path__`` if
``sys.path`` is altered after a namespace package has already been
created. However, existing namespace utilities (like
``pkgutil.extend_path``) can be used to update them explicitly if
desired.
Note that if "import foo" is executed and "foo" is found as a
namespace package (using the above rules), then "foo" is immediately
created as a package. The creation of the namespace package is not
deferred until a sub-level import occurs.
A namespace package is not fundamentally different from a regular
package. It is just a different way of creating packages. Once a
package. It is just a different way of creating packages. Once a
namespace package is created, there is no functional difference
between it and a regular package. The only observable difference is
that the namespace package's ``__file__`` attribute will end with a
path separator (typically a slash or backslash, depending on the
platform).
between it and a regular package.
Impact on Import Finders and Loaders
Dynamic path computation
------------------------
A namespace package's ``__path__`` will be recomputed if the value of
the parent path changes. In order for this feature to work, the parent
path must be modified in-place, not replaced with a new object. For
example, for top-level namespace packages, this will work::
sys.path.append('new-dir')
But this will not::
sys.path = sys.path + ['new-dir']
Impact on import finders and loaders
------------------------------------
PEP 302 defines "finders" that are called to search path elements.
These finders' ``find_module`` methods currently return either a
"loader" object or None. For a finder to contribute to namespace
packages, ``find_module`` will return a third type: a string. This is
the string that will be recorded and later used as a component of the
namespace module's ``__path__``, as described above. This string must
not contain a trailing path separator.
These finders' ``find_module`` methods return either a "loader" object
or ``None``.
For a finder to contribute to namespace packages, it must implement a
new ``find_loader(fullname)`` method. ``fullname`` has the same
meaning as for ``find_module``. ``find_loader`` always returns a
2-tuple of ``(loader, <iterable-of-path-entries>)``. ``loader`` may
be ``None``, in which case ``<iterable-of-path-entries>`` (which may
be empty) is added to the list of recorded path entries and path
searching continues. If ``loader`` is not ``None``, it is immediately
used to load a module or regular package.
Even if ``loader`` is returned and is not ``None``,
``<iterable-of-path-entries>`` must still contain the path entries for
the package. This allows code such as ``pkgutil.extend_path()`` to
compute path entries for packages that it does not load.
Note that multiple path entries per finder are allowed. This is to
support the case where a finder discovers multiple namespace portions
for a given ``fullname``. Many finders will support only a single
namespace package portion per ``find_loader`` call, in which case this
iterable will contain only a single string.
The import machinery will call ``find_loader`` if it exists, else fall
back to ``find_module``. Legacy finders which implement
``find_module`` but not ``find_loader`` will be unable to contribute
portions to a namespace package.
The specification expands PEP 302 loaders to include an optional method called
``module_repr()`` which if present, is used to generate module object reprs.
See the section below for further details.
If an existing finder is not updated to support returning a string
from ``find_module``, the only impact is that such a finder will be
unable to provide portions of a namespace package.
Differences between namespace packages and regular packages
-----------------------------------------------------------
Namespace packages and regular packages are very similar. The
differences are:
* Portions of namespace packages need not all come from the same
directory structure, or even from the same loader. Regular packages
are self-contained: all parts live in the same directory hierarchy.
* Namespace packages have no ``__file__`` attribute.
* Namespace packages' ``__path__`` attribute is a read-only iterable
of strings, which is automatically updated when the parent path is
modified.
* Namespace packages have no ``__init__.py`` module.
* Namespace packages have a different type of object for their
``__loader__`` attribute.
Namespace packages in the standard library
------------------------------------------
It is possible, and this PEP explicitly allows, that parts of the
standard library be implemented as namespace packages. When and if
any standard library packages become namespace packages is outside the
scope of this PEP.
Migrating from legacy namespace packages
----------------------------------------
As described above, prior to this PEP ``pkgutil.extend_path()`` was
used by legacy portions to create namespace packages. Because it is
likely not practical for all existing portions of a namespace package
to be migrated to this PEP at once, ``extend_path()`` will be modified
to also recognize PEP 420 namespace packages. This will allow some
portions of a namespace to be legacy portions while others are
migrated to PEP 420. These hybrid namespace packages will not have
the dynamic path computation that normal namespace packages have,
since ``extend_path()`` never provided this functionality in the past.
Packaging Implications
======================
@ -201,7 +274,7 @@ If the portions are installed in different locations, two different
"foo" directories would be in directories that are on ``sys.path``.
"foo/bar" would be in one of these sys.path entries, and "foo/baz"
would be in the other. Upon removal of "foo.bar", the "foo/bar" and
corresponding "foo" directories can be completely removed. But
corresponding "foo" directories can be completely removed. But
"foo/baz" and its corresponding "foo" directory cannot be removed.
It is also possible to have the "foo.bar" portion installed in a
@ -212,7 +285,7 @@ Discussion
==========
At PyCon 2012, we had a discussion about namespace packages at which
PEP 382 and PEP 402 were rejected, to be replaced by this PEP [2]_.
PEP 382 and PEP 402 were rejected, to be replaced by this PEP [3]_.
There is no intention to remove support of regular packages. If a
developer knows that her package will never be a portion of a
@ -227,7 +300,7 @@ lacking an ``__init__.py`` file. Such a directory will now be
imported as a namespace package, whereas in prior Python versions an
ImportWarning would be raised.
Nick Coghlan presented a list of his objections to this proposal [3]_.
Nick Coghlan presented a list of his objections to this proposal [4]_.
They are:
1. Implicit package directories go against the Zen of Python.
@ -239,9 +312,9 @@ They are:
layouts.
4. Implicit package directories will permanently entrench current
newbie-hostile behaviour in ``__main__``.
newbie-hostile behavior in ``__main__``.
Nick gave a detailed response [4]_, which is summarized here:
Nick gave a detailed response [5]_, which is summarized here:
1. The practicality of this PEP wins over other proposals and the
status quo.
@ -253,11 +326,25 @@ Nick gave a detailed response [4]_, which is summarized here:
4. This will also be addressed in PEP 395.
Phillip Eby asked about auto-updating of ``__path__``, instead of it
being a simple list [5]_. It is the intent of this PEP to get the
simplest possible solution working. It will be possible at a later
date to add such features. Several possible ways to do so were
discussed in the referenced email thread.
``find_module`` versus ``find_loader``
--------------------------------------
An early draft of this PEP specified a change to the ``find_module``
method in order to support namespace packages. It would be modified
to return a string in the case where a namespace package portion was
discovered.
However, this caused a problem with existing code outside of the
standard library which calls ``find_module``. Because this code would
not be upgraded in concert with changes required by this PEP, it would
fail when it would receive unexpected return values from
``find_module``. Because of this incompatibility, this PEP now
specifies that finders that want to provide namespace portions must
implement the ``find_loader`` method, described above.
The use case for supporting multiple portions per ``find_loader`` call
is given in [6]_.
Module reprs
============
@ -304,17 +391,20 @@ References
.. [1] PEP 420 branch (http://hg.python.org/features/pep-420)
.. [2] PyCon 2012 Namespace Package discussion outcome
.. [2] PEP 402's description of use cases for namespace packages
(http://www.python.org/dev/peps/pep-0402/#the-problem)
.. [3] PyCon 2012 Namespace Package discussion outcome
(http://mail.python.org/pipermail/import-sig/2012-March/000421.html)
.. [3] Nick Coghlan's objection to the lack of marker files or directories
.. [4] Nick Coghlan's objection to the lack of marker files or directories
(http://mail.python.org/pipermail/import-sig/2012-March/000423.html)
.. [4] Nick Coghlan's response to his initial objections
.. [5] Nick Coghlan's response to his initial objections
(http://mail.python.org/pipermail/import-sig/2012-April/000464.html)
.. [5] Phillip Eby's question about auto-updating __path__
(http://mail.python.org/pipermail/import-sig/2012-April/000468.html)
.. [6] Use case for multiple portions per ``find_loader`` call
(http://mail.python.org/pipermail/import-sig/2012-May/000585.html)
Copyright
=========

431
pep-0421.txt
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@ -34,7 +34,7 @@ this change is due to the emergence of Jython, IronPython, and PyPy as
viable alternate implementations of Python.
Consider, however, the nearly two decades of CPython-centric Python
(i.e. most of its existence). That focus had understandably
(i.e. most of its existence). That focus has understandably
contributed to quite a few CPython-specific artifacts both in the
standard library and exposed in the interpreter. Though the core
developers have made an effort in recent years to address this, quite
@ -51,41 +51,50 @@ Proposal
========
We will add a new attribute to the ``sys`` module, called
``sys.implementation``, as an instance of a new type to contain
implementation-specific information.
``sys.implementation``, as an object with attribute-access (as opposed
to a mapping). It will contain contain implementation-specific
information.
The attributes of this object will remain fixed during interpreter
execution and through the course of an implementation version. This
ensures behaviors don't change between versions which depend on
variables in ``sys.implementation``.
attributes of ``sys.implementation``.
The object will have each of the attributes described in the `Required
Variables`_ section below. Any other per-implementation values may be
stored in ``sys.implementation.metadata``. However, nothing in the
standard library will rely on ``sys.implementation.metadata``.
Examples of possible metadata values are described in the `Example
Metadata Values`_ section.
The object has each of the attributes described in the `Required
Attributes`_ section below. Those attribute names will never start
with an underscore. The standard library and the language definition
will rely only on those required attributes.
This proposal takes a conservative approach in requiring only four
variables. As more become appropriate, they may be added with
discretion.
This proposal takes a conservative approach in requiring only a small
number of attributes. As more become appropriate, they may be added
with discretion, as described in `Adding New Required Attributes`_.
While this PEP places no other constraints on ``sys.implementation``,
it also recommends that no one rely on capabilities outside those
described here. The only exception to that recommendation is for
attributes starting with an underscore. Implementors may use those
as appropriate to store per-implementation data.
Required Variables
------------------
Required Attributes
-------------------
These are variables in ``sys.implementation`` on which the standard
library would rely, with the exception of ``metadata``, meaning
implementers must define them:
These are attributes in ``sys.implementation`` on which the standard
library and language definition will rely, meaning implementers must
define them:
**name**
This is the common name of the implementation (case sensitive).
Examples include 'PyPy', 'Jython', 'IronPython', and 'CPython'.
A lower-case identifer representing the implementation. Examples
include 'pypy', 'jython', 'ironpython', and 'cpython'.
**version**
This is the version of the implementation, as opposed to the
version of the language it implements. This value conforms to the
format described in `Version Format`_.
The version of the implementation, as opposed to the version of the
language it implements. This value conforms to the format described
in `Version Format`_.
**hexversion**
The version of the implementation in the same hexadecimal format as
``sys.hexversion``.
**cache_tag**
A string used for the PEP 3147 cache tag [#cachetag]_. It would
@ -94,17 +103,21 @@ implementers must define them:
different cache tag. If ``cache_tag`` is set to None, it indicates
that module caching should be disabled.
**metadata**
Any other values that an implementation wishes to specify,
particularly informational ones. Neither the standard library nor
the language specification will rely on implementation metadata.
Also see the list of `Example Metadata Values`_.
Adding New Required Attributes
------------------------------
XXX PEP? something lighter?
In time more required attributes will be added to
``sys.implementation``. However, each must have a meaningful use case
across all Python implementations in order to be considered. This is
made most clear by a use case in the standard library or language
specification.
All proposals for new required attributes will go through the normal
PEP process. Such a PEP need not be long, just long enough. It will
need to sufficiently spell out the rationale for the new attribute,
its use cases, and the impact it will have on the various Python
implemenations.
Version Format
@ -112,59 +125,14 @@ Version Format
A main point of ``sys.implementation`` is to contain information that
will be used internally in the standard library. In order to
facilitate the usefulness of a version variable, its value should be
in a consistent format across implementations.
facilitate the usefulness of the version attribute, its value should
be in a consistent format across implementations.
As such, the format of ``sys.implementation.version`` must follow that
As such, the format of ``sys.implementation.version`` will follow that
of ``sys.version_info``, which is effectively a named tuple. It is a
familiar format and generally consistent with normal version format
conventions.
XXX The following is not exactly true:
Keep in mind, however, that ``sys.implementation.version`` is the
version of the Python *implementation*, while ``sys.version_info``
(and friends) is the version of the Python language.
Example Metadata Values
-----------------------
These are the sorts of values an implementation may put into
``sys.implementation.metadata``. However, these names and
descriptions are only examples and are not being proposed here. If
they later have meaningful uses cases, they can be added by following
the process described in `Adding New Required Attributes`_.
**vcs_url**
The URL pointing to the main VCS repository for the implementation
project.
**vcs_revision_id**
A value that identifies the VCS revision of the implementation that
is currently running.
**build_toolchain**
Identifies the tools used to build the interpreter.
**build_date**
The timestamp of when the interpreter was built.
**homepage**
The URL of the implementation's website.
**site_prefix**
The preferred site prefix for this implementation.
**runtime**
The run-time environment in which the interpreter is running, as
in "Common Language *Runtime*" (.NET CLR) or "Java *Runtime*
Executable".
**gc_type**
The type of garbage collection used, like "reference counting" or
"mark and sweep".
Rationale
=========
@ -179,87 +147,41 @@ the implementation-specific information into a single namespace and
makes explicit that which was implicit.
Why a Custom Type?
------------------
Type Considerations
-------------------
A dedicated class, of which ``sys.implementation`` is an instance, would
facilitate the dotted access of a "named" tuple. At the same time, it
allows us to avoid the problems of the other approaches (see below),
like confusion about ordering and iteration.
It's very easy to get bogged down in discussions about the type of
``sys.implementation``. However, its purpose is to support the
standard library and language definition. As such, there isn't much
that really matters regarding its type, as opposed to a feature that
would be more generally used. Thus characteristics like immutability
and sequence-ness have been disregarded.
The alternatives to a dictionary are considered separately here:
**Dictionary**
A dictionary reflects a simple namespace with item access. It
maps names to values and that's all. It also reflects the more variable
nature of ``sys.implementation``.
However, a simple dictionary does not set expectations very well about
the nature of ``sys.implementation``. The custom type approach, with
a fixed set of required attributes, does a better job of this.
**Named Tuple**
Another close alternative is a namedtuple or a structseq or some other
tuple type with dotted access (a la ``sys.version_info``). This type
is immutable and simple. It is a well established pattern for
implementation-specific variables in Python. Dotted access on a
namespace is also very convenient.
Fallback lookup may favor dicts::
cache_tag = sys.implementation.get('cache_tag')
vs.
cache_tag = getattr(sys.implementation.get, 'cache_tag', None)
However, this is mitigated by having ``sys.implementation.metadata``.
One problem with using a named tuple is that ``sys.implementation`` does
not have meaning as a sequence. Also, unlike other similar ``sys``
variables, it has a far greater potential to change over time.
If a named tuple were used, we'd be very clear in the documentation
that the length and order of the value are not reliable. Iterability
would not be guaranteed.
**Module**
Using a module instead of a dict is another option. It has similar
characteristics to an instance, but with a slight hint of immutability
(at least by convention). Such a module could be a stand-alone sub-
module of ``sys`` or added on, like ``os.path``. Unlike a concrete
class, no new type would be necessary. This is a pretty close fit to
what we need.
The downside is that the module type is much less conducive to
extension, making it more difficult to address the weaknesses of using
an instance of a concrete class.
The only real choice has been between an object with attribute access
and a mapping with item access. This PEP espouses dotted access to
reflect the relatively fixed nature of the namespace.
Why metadata?
-------------
Non-Required Attributes
-----------------------
``sys.implementation.metadata`` will hold any optional, strictly-
informational, or per-implementation data. This allows us to restrict
``sys.implementation`` to the required attributes. In that way, its
type can reflect the more stable namespace and
``sys.implementation.metadata`` (as a dict) can reflect the less
certain namespace.
Earlier versions of this PEP included a required attribute called
``metadata`` that held any non-required, per-implementation data
[#Nick]_. However, this proved to be an unnecessary addition
considering the purpose of ``sys.implementation``.
``sys.implementation.metadata`` is the place an implementation can put
values that must be built-in, "without having to pollute the main sys
namespace" [#Nick]_.
Ultimately, non-required attributes are virtually ignored in this PEP.
They have no impact other than that careless use may collide with
future required attributes. That, however, is but a marginal concern
for ``sys.implementation``.
Why a Part of ``sys``?
----------------------
The ``sys`` module should hold the new namespace because ``sys`` is
the depot for interpreter-centric variables and functions. Many
implementation-specific variables are already found in ``sys``.
The ``sys`` module holds the new namespace because ``sys`` is the depot
for interpreter-centric variables and functions. Many
implementation-specific attributes are already found in ``sys``.
Why Strict Constraints on Any of the Values?
@ -269,7 +191,8 @@ As already noted in `Version Format`_, values in
``sys.implementation`` are intended for use by the standard library.
Constraining those values, essentially specifying an API for them,
allows them to be used consistently, regardless of how they are
otherwise implemented.
otherwise implemented. However, care should be take to not
over-specify the constraints.
Discussion
@ -281,6 +204,9 @@ revived the discussion recently while working on a pure-python
``imp.get_tag()`` [#revived]_. Discussion has been ongoing
[#feedback]_. The messages in `issue #14673`_ are also relevant.
A good part of the recent discussion centered on the type to use for
``sys.implementation``.
Use-cases
=========
@ -290,10 +216,10 @@ platform.python_implementation()
"explicit is better than implicit"
The ``platform`` module determines the python implementation by
looking for clues in a couple different ``sys`` variables [#guess]_.
However, this approach is fragile, requiring changes to the standard
library each time an implementation changes. Beyond that, support in
The ``platform`` module determines the python implementation by looking
for clues in a couple different ``sys`` variables [#guess]_. However,
this approach is fragile, requiring changes to the standard library
each time an implementation changes. Beyond that, support in
``platform`` is limited to those implementations that core developers
have blessed by special-casing them in the ``platform`` module.
@ -302,7 +228,7 @@ With ``sys.implementation`` the various implementations would
module.
Another concern is that the ``platform`` module is part of the stdlib,
which ideally would minimize implementation details such as would be
which ideally should minimize implementation details such as would be
moved to ``sys.implementation``.
Any overlap between ``sys.implementation`` and the ``platform`` module
@ -359,47 +285,108 @@ In Jython, ``os.name`` is set to 'java' to accommodate special
treatment of the java environment in the standard library [#os_name]_
[#javatest]_. Unfortunately it masks the os name that would otherwise
go there. ``sys.implementation`` would help obviate the need for this
special case.
special case. Currently Jython sets ``os._name`` for the normal
``os.name`` value.
Feedback From Other Python Implementers
The Problem With ``sys.(version|version_info|hexversion)``
----------------------------------------------------------
Earlier versions of this PEP made the mistake of calling
``sys.version_info`` (and friends) the version of the Python language,
in contrast to the implementation. However, this is not the case.
Instead, it is the version of the CPython implementation. Incidently,
the first two components of ``sys.version_info`` (major and minor) also
reflect the version of the language definition.
As Barry Warsaw noted, the "semantics of sys.version_info have been
sufficiently squishy in the past" [#Barry]_. With
``sys.implementation`` we have the opportunity to improve this
situation by first establishing an explicit location for the version of
the implementation.
This PEP makes no other effort to directly clarify the semantics of
``sys.version_info``. Regardless, having an explicit version for the
implementation will definitely help to clarify the distinction from the
language version.
Feedback From Other Python Implementors
=======================================
IronPython
----------
XXX
Jeff Hardy responded to a request for feedback [#ironpython]_. He
said, "I'll probably add it the day after it's approved"
[#jeff_hardy_2012]_. He also gave useful feedback on both the type of
``sys.implementation`` and on the ``metadata`` attribute (which has
since been removed from the PEP).
Jython
------
XXX
In 2009 Frank Wierzbicki said this (relative to Jython implementing the
required attributes) [#frank_wierzbicki_2009]_::
Speaking for Jython, so far it looks like something we would adopt
soonish after it was accepted (it looks pretty useful to me).
PyPy
----
XXX
Some of the PyPy developers have responded to a request for feedback
[#pypy]_. Armin Rigo said the following [#armin_rigo_2012]_::
For myself, I can only say that it looks like a good idea, which we
will happily adhere to when we migrate to Python 3.3.
He also expressed support for keeping the required list small. Both
Armin and Laura Creighton indicated that an effort to better catalog
Python's implementation would be welcome. Such an effort, for which
this PEP is a small start, will be considered separately.
Past Efforts
============
PEP 3139
--------
``PEP 3139``
------------
This PEP from 2008 recommended a clean-up of the ``sys`` module in
PEP 3139, from 2008, recommended a clean-up of the ``sys`` module in
part by extracting implementation-specific variables and functions
into a separate module. PEP 421 is a much lighter version of that
into a separate module. PEP 421 is less ambitious version of that
idea. While PEP 3139 was rejected, its goals are reflected in PEP 421
to a large extent, though with a much lighter approach.
PEP 399
-------
``PEP 399``
-----------
This informational PEP dictates policy regarding the standard library,
helping to make it friendlier to alternate implementations. PEP 421
is proposed in that same spirit.
PEP 399 dictates policy regarding the standard library, helping to make
it friendlier to alternate implementations. PEP 421 is proposed in
that same spirit.
The Bigger Picture
==================
It's worth noting again that this PEP is a small part of a larger
on-going effort to identify the implementation-specific parts of Python
and mitigate their impact on alternate implementations.
``sys.implementation`` is a focal point for implementation-specific
data, acting as a nexus for cooperation between the language, the
standard library, and the different implementations. As time goes by
it is feasible that ``sys.implementation`` will assume current
attributes of ``sys`` and other builtin/stdlib modules, where
appropriate. In this way, it is a PEP 3137-lite, but starting as
small as possible.
However, as already noted, many other efforts predate
``sys.implementation``. Neither is it necessarily a major part of the
effort. Rather, consider it as part of the infrastructure of the
effort to make Python friendler to alternate implementations.
Alternatives
@ -409,50 +396,49 @@ Since the single-namespace-under-sys approach is relatively
straightforward, no alternatives have been considered for this PEP.
Examples of Other Attributes
============================
These are examples only and not part of the proposal. Most of them
were suggested during previous discussions, but did not fit into the
goals of this PEP. (See `Adding New Required Attributes`_ if they get
you excited.)
**common_name**
The case-sensitive name by which the implementation is known.
**vcs_url**
A URL for the main VCS repository for the implementation project.
**vcs_revision_id**
A value that identifies the VCS revision of the implementation.
**build_toolchain**
The tools used to build the interpreter.
**build_date**
The timestamp of when the interpreter was built.
**homepage**
The URL of the implementation's website.
**site_prefix**
The preferred site prefix for the implementation.
**runtime**
The run-time environment in which the interpreter is running, as
in "Common Language *Runtime*" (.NET CLR) or "Java *Runtime*
Executable".
**gc_type**
The type of garbage collection used, like "reference counting" or
"mark and sweep".
Open Issues
===========
* What are the long-term objectives for ``sys.implementation``?
- possibly pull in implementation details from the main ``sys``
namespace and elsewhere (PEP 3137 lite).
* What is the process for introducing new required variables? PEP?
* Is the ``sys.version_info`` format the right one here?
* Should ``sys.implementation.hexversion`` be part of the PEP?
* Does ``sys.(version|version_info|hexversion)`` need to better
reflect the version of the language spec? Micro version, series,
and release seem like implementation-specific values.
* Alternatives to the approach dictated by this PEP?
* Do we really want to commit to using a dict for
``sys.implementation``?
Backward compatibility issues will make it difficult to change our
minds later.
The type we use ultimately depends on how general we expect the
consumption of ``sys.implementation`` to be. If its practicality is
oriented toward internal use then the data structure is not as
critical. However, ``sys.implementation`` is intended to have a
non-localized impact across the standard library and the
interpreter. It is better to *not* make hacking it become an
attractive nuisance, regardless of our intentions for usage.
* Should ``sys.implementation`` and its values be immutable? A benefit
of an immutable type is it communicates that the value is not
expected to change and should not be manipulated.
* Should ``sys.implementation`` be strictly disallowed to have methods?
Classes often imply the presence (or possibility) of methods, which
may be misleading in this case.
* Should ``sys.implementation`` implement the collections.abc.Mapping
interface?
Currently none.
Implementation
@ -468,11 +454,33 @@ References
http://mail.python.org/pipermail/python-dev/2009-October/092893.html
.. [#revived] The initial 2012 discussion:
http://mail.python.org/pipermail/python-ideas/2012-April/014878.html
http://mail.python.org/pipermail/python-ideas/2012-March/014555.html
(and http://mail.python.org/pipermail/python-ideas/2012-April/014878.html)
.. [#feedback] Feedback on the PEP:
http://mail.python.org/pipermail/python-ideas/2012-April/014954.html
.. [#ironpython] Feedback from the IronPython developers:
http://mail.python.org/pipermail/ironpython-users/2012-May/015980.html
.. [#dino_viehland_2009] (2009) Dino Viehland offers his opinion:
http://mail.python.org/pipermail/python-dev/2009-October/092894.html
.. [#jeff_hardy_2012] (2012) Jeff Hardy offers his opinion:
http://mail.python.org/pipermail/ironpython-users/2012-May/015981.html
.. [#jython] Feedback from the Jython developers:
???
.. [#frank_wierzbicki_2009] (2009) Frank Wierzbicki offers his opinion:
http://mail.python.org/pipermail/python-dev/2009-October/092974.html
.. [#pypy] Feedback from the PyPy developers:
http://mail.python.org/pipermail/pypy-dev/2012-May/009883.html
.. [#armin_rigo_2012] (2012) Armin Rigo offers his opinion:
http://mail.python.org/pipermail/pypy-dev/2012-May/009884.html
.. [#guess] The ``platform`` code which divines the implementation name:
http://hg.python.org/cpython/file/2f563908ebc5/Lib/platform.py#l1247
@ -497,6 +505,9 @@ References
.. [#Nick] Nick Coghlan's proposal for ``sys.implementation.metadata``:
http://mail.python.org/pipermail/python-ideas/2012-May/014984.html
.. [#Barry] Feedback from Barry Warsaw:
http://mail.python.org/pipermail/python-dev/2012-May/119374.html
.. _issue #14673: http://bugs.python.org/issue14673
.. _Lib/test/support.py: http://hg.python.org/cpython/file/2f563908ebc5/Lib/test/support.py

43
pep-3144.txt
View File

@ -5,30 +5,36 @@ Last-Modified: $Date$
Author: Peter Moody <pmoody@google.com>
BDFL-Delegate: Nick Coghlan
Discussions-To: <ipaddr-py-dev@googlegroups.com>
Status: Draft
Status: Accepted
Type: Standards Track
Content-Type: text/plain
Created: 6-Feb-2012
Python-Version: 3.3
Resolution: http://mail.python.org/pipermail/python-dev/2012-May/119474.html
Abstract:
This PEP proposes a design and for an IP address manipulation module for
python.
PEP Acceptance:
This PEP was accepted by Nick Coghlan on the 15th of May, 2012.
Motivation:
Several very good IP address modules for python already exist.
The truth is that all of the struggle with the balance between
The truth is that all of them struggle with the balance between
adherence to Pythonic principals and the shorthand upon which
network engineers and administrators rely. I believe ipaddr
strikes the right balance.
network engineers and administrators rely. ipaddress aims to
strike the right balance.
Rationale:
The existance of several Python IP address manipulation moduels is
The existence of several Python IP address manipulation modules is
evidence of an outstanding need for the functionality this module
seeks to provide.
@ -55,6 +61,23 @@ Background:
* A few attributes were renamed to disambiguate their purpose as
well. (eg. network, network_address)
* A number of methods and functions which returned containers in ipaddr now
return iterators. This includes, subnets, address_exclude,
summarize_address_range and collapse_address_list.
Due to the backwards incompatible API changes between ipaddress and ipaddr,
the proposal is to add the module using the new provisional API status:
* http://docs.python.org/dev/glossary.html#term-provisional-package
Relevant messages on python-dev:
* http://mail.python.org/pipermail/python-dev/2012-January/116016.html
* http://mail.python.org/pipermail/python-dev/2012-February/116656.html
* http://mail.python.org/pipermail/python-dev/2012-February/116688.html
Specification:
@ -101,8 +124,7 @@ Specification:
_BaseV4 - Provides methods and variables (eg, _max_prefixlen)
common to all IPv4 classes.
_BaseV6 - Provides methods and variables common to all IPv6
classes.
_BaseV6 - Provides methods and variables common to all IPv6 classes.
Comparisons between objects of differing IP versions results in a
TypeError [1]. Additionally, comparisons of objects with
@ -115,7 +137,10 @@ Specification:
Reference Implementation:
The current reference implementation can be found at:
http://code.google.com/p/ipaddr-py/downloads/detail?name=3144.tar.gz
http://code.google.com/p/ipaddress-py/source/browse/ipaddress.py
Or see the tarball to include the README and unittests.
http://code.google.com/p/ipaddress-py/downloads/detail?name=ipaddress-1.0.tar.gz
More information about using the reference implementation can be
found at: http://code.google.com/p/ipaddr-py/wiki/Using3144