It has been a while since I posted a copy of PEP 1 to the mailing
lists and newsgroups. I've recently done some updating of a few
sections, so in the interest of gaining wider community participation
in the Python development process, I'm posting the latest revision of
PEP 1 here. A version of the PEP is always available on-line at
-------------------- snip snip --------------------
Title: PEP Purpose and Guidelines
Version: $Revision: 1.36 $
Last-Modified: $Date: 2002/07/29 18:34:59 $
Author: Barry A. Warsaw, Jeremy Hylton
Post-History: 21-Mar-2001, 29-Jul-2002
What is a PEP?
PEP stands for Python Enhancement Proposal. A PEP is a design
document providing information to the Python community, or
describing a new feature for Python. The PEP should provide a
concise technical specification of the feature and a rationale for
We intend PEPs to be the primary mechanisms for proposing new
features, for collecting community input on an issue, and for
documenting the design decisions that have gone into Python. The
PEP author is responsible for building consensus within the
community and documenting dissenting opinions.
Because the PEPs are maintained as plain text files under CVS
control, their revision history is the historical record of the
Kinds of PEPs
There are two kinds of PEPs. A standards track PEP describes a
new feature or implementation for Python. An informational PEP
describes a Python design issue, or provides general guidelines or
information to the Python community, but does not propose a new
feature. Informational PEPs do not necessarily represent a Python
community consensus or recommendation, so users and implementors
are free to ignore informational PEPs or follow their advice.
PEP Work Flow
The PEP editor, Barry Warsaw <peps(a)python.org>, assigns numbers
for each PEP and changes its status.
The PEP process begins with a new idea for Python. It is highly
recommended that a single PEP contain a single key proposal or new
idea. The more focussed the PEP, the more successfully it tends
to be. The PEP editor reserves the right to reject PEP proposals
if they appear too unfocussed or too broad. If in doubt, split
your PEP into several well-focussed ones.
Each PEP must have a champion -- someone who writes the PEP using
the style and format described below, shepherds the discussions in
the appropriate forums, and attempts to build community consensus
around the idea. The PEP champion (a.k.a. Author) should first
attempt to ascertain whether the idea is PEP-able. Small
enhancements or patches often don't need a PEP and can be injected
into the Python development work flow with a patch submission to
the SourceForge patch manager or feature request tracker.
The PEP champion then emails the PEP editor <peps(a)python.org> with
a proposed title and a rough, but fleshed out, draft of the PEP.
This draft must be written in PEP style as described below.
If the PEP editor approves, he will assign the PEP a number, label
it as standards track or informational, give it status 'draft',
and create and check-in the initial draft of the PEP. The PEP
editor will not unreasonably deny a PEP. Reasons for denying PEP
status include duplication of effort, being technically unsound,
not providing proper motivation or addressing backwards
compatibility, or not in keeping with the Python philosophy. The
BDFL (Benevolent Dictator for Life, Guido van Rossum) can be
consulted during the approval phase, and is the final arbitrator
of the draft's PEP-ability.
If a pre-PEP is rejected, the author may elect to take the pre-PEP
to the comp.lang.python newsgroup (a.k.a. python-list(a)python.org
mailing list) to help flesh it out, gain feedback and consensus
from the community at large, and improve the PEP for
The author of the PEP is then responsible for posting the PEP to
the community forums, and marshaling community support for it. As
updates are necessary, the PEP author can check in new versions if
they have CVS commit permissions, or can email new PEP versions to
the PEP editor for committing.
Standards track PEPs consists of two parts, a design document and
a reference implementation. The PEP should be reviewed and
accepted before a reference implementation is begun, unless a
reference implementation will aid people in studying the PEP.
Standards Track PEPs must include an implementation - in the form
of code, patch, or URL to same - before it can be considered
PEP authors are responsible for collecting community feedback on a
PEP before submitting it for review. A PEP that has not been
discussed on python-list(a)python.org and/or python-dev(a)python.org
will not be accepted. However, wherever possible, long open-ended
discussions on public mailing lists should be avoided. Strategies
to keep the discussions efficient include, setting up a separate
SIG mailing list for the topic, having the PEP author accept
private comments in the early design phases, etc. PEP authors
should use their discretion here.
Once the authors have completed a PEP, they must inform the PEP
editor that it is ready for review. PEPs are reviewed by the BDFL
and his chosen consultants, who may accept or reject a PEP or send
it back to the author(s) for revision.
Once a PEP has been accepted, the reference implementation must be
completed. When the reference implementation is complete and
accepted by the BDFL, the status will be changed to `Final.'
A PEP can also be assigned status `Deferred.' The PEP author or
editor can assign the PEP this status when no progress is being
made on the PEP. Once a PEP is deferred, the PEP editor can
re-assign it to draft status.
A PEP can also be `Rejected'. Perhaps after all is said and done
it was not a good idea. It is still important to have a record of
PEPs can also be replaced by a different PEP, rendering the
original obsolete. This is intended for Informational PEPs, where
version 2 of an API can replace version 1.
PEP work flow is as follows:
Draft -> Accepted -> Final -> Replaced
Some informational PEPs may also have a status of `Active' if they
are never meant to be completed. E.g. PEP 1.
What belongs in a successful PEP?
Each PEP should have the following parts:
1. Preamble -- RFC822 style headers containing meta-data about the
PEP, including the PEP number, a short descriptive title
(limited to a maximum of 44 characters), the names, and
optionally the contact info for each author, etc.
2. Abstract -- a short (~200 word) description of the technical
issue being addressed.
3. Copyright/public domain -- Each PEP must either be explicitly
labelled as placed in the public domain (see this PEP as an
example) or licensed under the Open Publication License.
4. Specification -- The technical specification should describe
the syntax and semantics of any new language feature. The
specification should be detailed enough to allow competing,
interoperable implementations for any of the current Python
platforms (CPython, JPython, Python .NET).
5. Motivation -- The motivation is critical for PEPs that want to
change the Python language. It should clearly explain why the
existing language specification is inadequate to address the
problem that the PEP solves. PEP submissions without
sufficient motivation may be rejected outright.
6. Rationale -- The rationale fleshes out the specification by
describing what motivated the design and why particular design
decisions were made. It should describe alternate designs that
were considered and related work, e.g. how the feature is
supported in other languages.
The rationale should provide evidence of consensus within the
community and discuss important objections or concerns raised
7. Backwards Compatibility -- All PEPs that introduce backwards
incompatibilities must include a section describing these
incompatibilities and their severity. The PEP must explain how
the author proposes to deal with these incompatibilities. PEP
submissions without a sufficient backwards compatibility
treatise may be rejected outright.
8. Reference Implementation -- The reference implementation must
be completed before any PEP is given status 'Final,' but it
need not be completed before the PEP is accepted. It is better
to finish the specification and rationale first and reach
consensus on it before writing code.
The final implementation must include test code and
documentation appropriate for either the Python language
reference or the standard library reference.
PEPs are written in plain ASCII text, and should adhere to a
rigid style. There is a Python script that parses this style and
converts the plain text PEP to HTML for viewing on the web.
PEP 9 contains a boilerplate template you can use to get
started writing your PEP.
Each PEP must begin with an RFC822 style header preamble. The
headers must appear in the following order. Headers marked with
`*' are optional and are described below. All other headers are
PEP: <pep number>
Title: <pep title>
Version: <cvs version string>
Last-Modified: <cvs date string>
Author: <list of authors' real names and optionally, email addrs>
* Discussions-To: <email address>
Status: <Draft | Active | Accepted | Deferred | Final | Replaced>
Type: <Informational | Standards Track>
* Requires: <pep numbers>
Created: <date created on, in dd-mmm-yyyy format>
* Python-Version: <version number>
Post-History: <dates of postings to python-list and python-dev>
* Replaces: <pep number>
* Replaced-By: <pep number>
The Author: header lists the names and optionally, the email
addresses of all the authors/owners of the PEP. The format of the
author entry should be
address(a)dom.ain (Random J. User)
if the email address is included, and just
Random J. User
if the address is not given. If there are multiple authors, each
should be on a separate line following RFC 822 continuation line
conventions. Note that personal email addresses in PEPs will be
obscured as a defense against spam harvesters.
Standards track PEPs must have a Python-Version: header which
indicates the version of Python that the feature will be released
with. Informational PEPs do not need a Python-Version: header.
While a PEP is in private discussions (usually during the initial
Draft phase), a Discussions-To: header will indicate the mailing
list or URL where the PEP is being discussed. No Discussions-To:
header is necessary if the PEP is being discussed privately with
the author, or on the python-list or python-dev email mailing
lists. Note that email addresses in the Discussions-To: header
will not be obscured.
Created: records the date that the PEP was assigned a number,
while Post-History: is used to record the dates of when new
versions of the PEP are posted to python-list and/or python-dev.
Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2001.
PEPs may have a Requires: header, indicating the PEP numbers that
this PEP depends on.
PEPs may also have a Replaced-By: header indicating that a PEP has
been rendered obsolete by a later document; the value is the
number of the PEP that replaces the current document. The newer
PEP must have a Replaces: header containing the number of the PEP
that it rendered obsolete.
PEP Formatting Requirements
PEP headings must begin in column zero and the initial letter of
each word must be capitalized as in book titles. Acronyms should
be in all capitals. The body of each section must be indented 4
spaces. Code samples inside body sections should be indented a
further 4 spaces, and other indentation can be used as required to
make the text readable. You must use two blank lines between the
last line of a section's body and the next section heading.
You must adhere to the Emacs convention of adding two spaces at
the end of every sentence. You should fill your paragraphs to
column 70, but under no circumstances should your lines extend
past column 79. If your code samples spill over column 79, you
should rewrite them.
Tab characters must never appear in the document at all. A PEP
should include the standard Emacs stanza included by example at
the bottom of this PEP.
A PEP must contain a Copyright section, and it is strongly
recommended to put the PEP in the public domain.
When referencing an external web page in the body of a PEP, you
should include the title of the page in the text, with a
footnote reference to the URL. Do not include the URL in the body
text of the PEP. E.g.
Refer to the Python Language web site  for more details.
When referring to another PEP, include the PEP number in the body
text, such as "PEP 1". The title may optionally appear. Add a
footnote reference that includes the PEP's title and author. It
may optionally include the explicit URL on a separate line, but
only in the References section. Note that the pep2html.py script
will calculate URLs automatically, e.g.:
Refer to PEP 1  for more information about PEP style
 PEP 1, PEP Purpose and Guidelines, Warsaw, Hylton
If you decide to provide an explicit URL for a PEP, please use
this as the URL template:
PEP numbers in URLs must be padded with zeros from the left, so as
to be exactly 4 characters wide, however PEP numbers in text are
Reporting PEP Bugs, or Submitting PEP Updates
How you report a bug, or submit a PEP update depends on several
factors, such as the maturity of the PEP, the preferences of the
PEP author, and the nature of your comments. For the early draft
stages of the PEP, it's probably best to send your comments and
changes directly to the PEP author. For more mature, or finished
PEPs you may want to submit corrections to the SourceForge bug
manager or better yet, the SourceForge patch manager so that
your changes don't get lost. If the PEP author is a SF developer,
assign the bug/patch to him, otherwise assign it to the PEP
When in doubt about where to send your changes, please check first
with the PEP author and/or PEP editor.
PEP authors who are also SF committers, can update the PEPs
themselves by using "cvs commit" to commit their changes.
Remember to also push the formatted PEP text out to the web by
doing the following:
% python pep2html.py -i NUM
where NUM is the number of the PEP you want to push out. See
% python pep2html.py --help
Transferring PEP Ownership
It occasionally becomes necessary to transfer ownership of PEPs to
a new champion. In general, we'd like to retain the original
author as a co-author of the transferred PEP, but that's really up
to the original author. A good reason to transfer ownership is
because the original author no longer has the time or interest in
updating it or following through with the PEP process, or has
fallen off the face of the 'net (i.e. is unreachable or not
responding to email). A bad reason to transfer ownership is
because you don't agree with the direction of the PEP. We try to
build consensus around a PEP, but if that's not possible, you can
always submit a competing PEP.
If you are interested assuming ownership of a PEP, send a message
asking to take over, addressed to both the original author and the
PEP editor <peps(a)python.org>. If the original author doesn't
respond to email in a timely manner, the PEP editor will make a
unilateral decision (it's not like such decisions can be
References and Footnotes
 This historical record is available by the normal CVS commands
for retrieving older revisions. For those without direct access
to the CVS tree, you can browse the current and past PEP revisions
via the SourceForge web site at
 The script referred to here is pep2html.py, which lives in
the same directory in the CVS tree as the PEPs themselves.
Try "pep2html.py --help" for details.
The URL for viewing PEPs on the web is
 PEP 9, Sample PEP Template
This document has been placed in the public domain.
I've received some enthusiastic emails from someone who wants to
revive restricted mode. He started out with a bunch of patches to the
CPython runtime using ctypes, which he attached to an App Engine bug:
Based on his code (the file secure.py is all you need, included in
secure.tar.gz) it seems he believes the only security leaks are
__subclasses__, gi_frame and gi_code. (I have since convinced him that
if we add "restricted" guards to these attributes, he doesn't need the
functions added to sys.)
I don't recall the exploits that Samuele once posted that caused the
death of rexec.py -- does anyone recall, or have a pointer to the
--Guido van Rossum (home page: http://www.python.org/~guido/)
Alright, I will re-submit with the contents pasted. I never use double
backquotes as I think them rather ugly; that is the work of an editor
or some automated program in the chain. Plus, it also messed up my
line formatting and now I have lines with one word on them... Anyway,
the contents of PEP 3145:
Title: Asynchronous I/O For subprocess.Popen
Author: (James) Eric Pruitt, Charles R. McCreary, Josiah Carlson
Type: Standards Track
In its present form, the subprocess.Popen implementation is prone to
dead-locking and blocking of the parent Python script while waiting on data
from the child process.
A search for "python asynchronous subprocess" will turn up numerous
accounts of people wanting to execute a child process and communicate with
it from time to time reading only the data that is available instead of
blocking to wait for the program to produce data   . The current
behavior of the subprocess module is that when a user sends or receives
data via the stdin, stderr and stdout file objects, dead locks are common
and documented  . While communicate can be used to alleviate some of
the buffering issues, it will still cause the parent process to block while
attempting to read data when none is available to be read from the child
There is a documented need for asynchronous, non-blocking functionality in
subprocess.Popen    . Inclusion of the code would improve the
utility of the Python standard library that can be used on Unix based and
Windows builds of Python. Practically every I/O object in Python has a
file-like wrapper of some sort. Sockets already act as such and for
strings there is StringIO. Popen can be made to act like a file by simply
using the methods attached the the subprocess.Popen.stderr, stdout and
stdin file-like objects. But when using the read and write methods of
those options, you do not have the benefit of asynchronous I/O. In the
proposed solution the wrapper wraps the asynchronous methods to mimic a
I have been maintaining a Google Code repository that contains all of my
changes including tests and documentation  as well as blog detailing
the problems I have come across in the development process .
I have been working on implementing non-blocking asynchronous I/O in the
subprocess.Popen module as well as a wrapper class for subprocess.Popen
that makes it so that an executed process can take the place of a file by
duplicating all of the methods and attributes that file objects have.
There are two base functions that have been added to the subprocess.Popen
class: Popen.send and Popen._recv, each with two separate implementations,
one for Windows and one for Unix based systems. The Windows
implementation uses ctypes to access the functions needed to control pipes
in the kernel 32 DLL in an asynchronous manner. On Unix based systems,
the Python interface for file control serves the same purpose. The
different implementations of Popen.send and Popen._recv have identical
arguments to make code that uses these functions work across multiple
When calling the Popen._recv function, it requires the pipe name be
passed as an argument so there exists the Popen.recv function that passes
selects stdout as the pipe for Popen._recv by default. Popen.recv_err
selects stderr as the pipe by default. "Popen.recv" and "Popen.recv_err"
are much easier to read and understand than "Popen._recv('stdout' ..." and
"Popen._recv('stderr' ..." respectively.
Since the Popen._recv function does not wait on data to be produced
before returning a value, it may return empty bytes. Popen.asyncread
handles this issue by returning all data read over a given time
The ProcessIOWrapper class uses the asyncread and asyncwrite functions to
allow a process to act like a file so that there are no blocking issues
that can arise from using the stdout and stdin file objects produced from
a subprocess.Popen call.
 [ python-Feature Requests-1191964 ] asynchronous Subprocess
 Daily Life in an Ivory Basement : /feb-07/problems-with-subprocess
 How can I run an external command asynchronously from Python? - Stack
 18.1. subprocess - Subprocess management - Python v2.6.2 documentation
 18.1. subprocess - Subprocess management - Python v2.6.2 documentation
 Issue 1191964: asynchronous Subprocess - Python tracker
 Module to allow Asynchronous subprocess use on Windows and Posix
platforms - ActiveState Code
 subprocess.rst - subprocdev - Project Hosting on Google Code
 subprocdev - Project Hosting on Google Code
 Python Subprocess Dev
This P.E.P. is licensed under the Open Publication License;
On Tue, Sep 8, 2009 at 22:56, Benjamin Peterson <benjamin(a)python.org> wrote:
> 2009/9/7 Eric Pruitt <eric.pruitt(a)gmail.com>:
>> Hello all,
>> I have been working on adding asynchronous I/O to the Python
>> subprocess module as part of my Google Summer of Code project. Now
>> that I have finished documenting and pruning the code, I present PEP
>> 3145 for its inclusion into the Python core code. Any and all feedback
>> on the PEP (http://www.python.org/dev/peps/pep-3145/) is appreciated.
> Hi Eric,
> One of the reasons you're not getting many response is that you've not
> pasted the contents of the PEP in this message. That makes it really
> easy for people to comment on various sections.
> BTW, it seems like you were trying to use reST formatting with the
> text PEP layout. Double backquotes only mean something in reST.
Which I noticed since it's cited in the BeOpen license we still refer
to in LICENSE. Since pythonlabs.com itself is still up, it probably
isn't much work to make the logos.html URI work again, but I don't know
who maintains that page.
Thus spake the Lord: Thou shalt indent with four spaces. No more, no less.
Four shall be the number of spaces thou shalt indent, and the number of thy
indenting shall be four. Eight shalt thou not indent, nor either indent thou
two, excepting that thou then proceed to four. Tabs are right out.
[I've got no response from python-ideas, so I am forwarding to python-dev.]
With addition of fixed offset timezone class and the timezone.utc
instance , it is easy to get UTC time as an aware datetime
datetime.datetime(2010, 8, 3, 14, 16, 10, 670308, tzinfo=datetime.timezone.utc)
However, if you want to keep time in your local timezone, getting an
aware datetime is almost a catch 22. If you know your timezone UTC
offset, you can do
>>> EDT = timezone(timedelta(hours=-4))
datetime.datetime(2010, 8, 3, 10, 20, 23, 769537,
but the problem is that there is no obvious or even correct way to
find local timezone UTC offset. 
In a comment on issue #5094 ("datetime lacks concrete tzinfo
implementation for UTC"), I proposed to address this problem in a
localtime([t]) function that would return current time (or time
corresponding to the optional datetime argument) as an aware datetime
object carrying local timezone information in a tzinfo set to an
appropriate timezone instance. This solution is attractive by its
simplicity, but there are several problems:
1. An aware datetime cannot carry all information that system
localtime() supplies in a time tuple. Specifically, the is_dst flag
is lost. This is not a problem for most applications as long as
timezone UTC offset and timezone name are available, but may be an
issue when interoperability with the time module is required.
2. Datetime's tzinfo interface was designed with the idea that
<2010-11-06 12:00 EDT> + <1 day> = <2010-11-07 12:00 EST>, not
<2010-11-07 12:00 EDT>. It other words, if I have lunch with someone
at noon (12:00 EDT) on Saturday the day before first Sunday in
November, and want to meet again "at the same time tomorrow", I mean
12:00 EST, not 24 hours later. With localtime() returning datetime
with tzinfo set to fixed offset timezone, however, localtime() +
timedelta(1) will mean exactly 24 hours later and the result will be
expressed in an unusual for the given location timezone.
An alternative approach is the one recommended in the python manual.
 One could implement a LocalTimezone class with utcoffset(),
tzname() and dst() extracting information from system mktime and
localtime calls. This approach has its own shortcomings:
1. While adding integral number of days to datetimes in business
setting, it is natural to expect automatic timezone adjustments, it is
not as clearcut when adding hours or minutes.
2. The tzinfo.utcoffset() interface that expects *standard* local time
as an argument is confusing to many users. Even the "official"
example in the python manual gets it wrong. 
3. datetime(..., tzinfo=LocalTimezone()) is ambiguous during the
"repeated hour" when local clock is set back in DST to standard time
As far as I can tell, the only way to resolve the last problem is to
add is_dst flag to the datetime object, which would also be the
only way to achieve full interoperability between datetime objects and
time tuples. 
The traditional answer to call for improvement of timezone support in
datetime module has been: "this is upto 3rd parties to implement."
Unfortunately, stdlib is asking 3rd parties to implement an impossible
interface without giving access to the necessary data. The
impossibility comes from the requirement that dst() method should find
out whether local time represents DST or standard time while there is
an hour each year when the same local time can be either. The missing
data is the system UTC offset when it changes historically. The time
module only gives access to the current UTC offset.
My preference is to implement the first alternative - localtime([t])
returning aware datetime with fixed offset timezone. This will solve
the problem of python's lack of access to the universally available
system facilities that are necessary to implement any kind of aware
local time support.
I see several problems with the two hex-conversion function pairs that
1. binascii.hexlify and binascii.unhexlify
2. bytes.fromhex and bytes.hex
bytes.hex is not implemented, although it was specified in PEP 358.
This means there is no symmetrical function to accompany bytes.fromhex.
Both pairs perform the same function, although The Zen Of Python suggests
"There should be one-- and preferably only one --obvious way to do it."
I do not understand why PEP 358 specified the bytes function pair although
it mentioned the binascii pair...
bytes.fromhex may receive spaces in the input string, although
binascii.unhexlify may not.
I see no good reason for these two functions to have different features.
binascii.unhexlify may receive both input types: strings or bytes, whereas
bytes.fromhex raises an exception when given a bytes parameter.
Again there is no reason for these functions to be different.
binascii.hexlify returns a bytes type - although ideally, converting to hex
always return string types and converting from hex should always return
IMO there is no meaning of bytes as an output of hexlify, since the output
representation of other bytes.
This is also the suggested behavior of bytes.hex in PEP 358
Problems #4 and #5 call for a decision about the input and output of the
functions being discussed:
Option A : Strict input and output
unhexlify (and bytes.fromhex) may only receives string and may only return
hexlify (and bytes.hex) may only receives bytes and may only return strings
Option B : Robust input and strict output
unhexlify (and bytes.fromhex) may receive bytes and strings and may only
hexlify (and bytes.hex) may receive bytes or strings and may only return
Of course we may also consider a third option, which will allow the return
all functions to be robust (perhaps specified in a keyword argument), but as
I wrote in
the description of problem #5, I see no sense in that.
Note that PEP 3137 describes: "... the more strict definitions of encoding
and decoding in
Python 3000: encoding always takes a Unicode string and returns a bytes
sequence, and decoding
always takes a bytes sequence and returns a Unicode string." - suggesting
To repeat problems #4 and #5, the current behavior does not match any
* The return type of binascii.hexlify should be string, and this is not the
As for the input:
* Option A is not the current behavior because binascii.unhexlify may
receive both input types.
* Option B is not the current behavior because bytes.fromhex does not allow
bytes as input.
To fix these issues, three changes should be applied:
1. Deprecate bytes.fromhex. This fixes the following problems:
#4 (go with option B and remove the function that does not allow bytes
#2 (the binascii functions will be the only way to "do it")
#1 (bytes.hex should not be implemented)
2. In order to keep the functionality that bytes.fromhex has over unhexlify,
the latter function should be able to handle spaces in its input (fix #3)
3. binascii.hexlify should return string as its return type (fix #5)
I have now started an initial patch for PEP 384, in the pep-0384 branch.
This has the following features:
- modules can be compiled under Py_LIMITED_API
- Tools/scripts/abitype.py converts C code containing static
PyTypeObject definitions to use the new API for type definitions.
The following aspects are still missing:
- there is no support for generating python3.dll on Windows yet
- there has been no validation whether the API is actually feasible
to use in extension modules.
I started looking into porting the sqlite extension, and ran into
- certain fields of PyTypeObject are called directly:
- PyObject_Print is used, but can't be supported, as it uses a FILE*
For the first issue, it would be possible to provide a generic
accessor function that fetches fields from a type object. Alternatively,
each case could be considered, suggesting an alternative code for the
I'll be off the net for the next two weeks most of the time, so
I might not be able to respond quickly.
Anybody interested in advancing that patch, feel free to commit
changes into the branch.
This is a follow up to PEP 3147. That PEP, already implemented in Python 3.2,
allows for Python source files from different Python versions to live together
in the same directory. It does this by putting a magic tag in the .pyc file
name and placing the .pyc file in a __pycache__ directory.
Distros such as Debian and Ubuntu will use this to greatly simplifying
deploying Python, and Python applications and libraries. Debian and Ubuntu
usually ship more than one version of Python, and currently have to play
complex games with symlinks to make this work. PEP 3147 will go a long way to
eliminating the need for extra directories and symlinks.
One more thing I've found we need though, is a way to handled shared libraries
for extension modules. Just as we can get name collisions on foo.pyc, we can
get collisions on foo.so. We obviously cannot install foo.so built for Python
3.2 and foo.so built for Python 3.3 in the same location. So symlink
nightmare's mini-me is back.
I have a fairly simple fix for this. I'd actually be surprised if this hasn't
been discussed before, but teh Googles hasn't turned up anything.
The idea is to put the Python version number in the shared library file name,
and extend .so lookup to find these extended file names. So for example, we'd
see foo.3.2.so instead, and Python would know how to dynload both that and the
traditional foo.so file too (for backward compatibility).
(On file naming: the original patch used foo.so.3.2 and that works just as
well, but I thought there might be tools that expect exactly a '.so' suffix,
so I changed it to put the Major.Minor version number to the left of the
extension. The exact naming scheme is of course open to debate.)
This is a much simpler patch than PEP 3147, though I'm not 100% sure it's the
right approach. The way this works is by modifying the configure and
Makefile.pre.in to put the version number in the $SO make variable. Python
parses its (generated) Makefile to find $SO and it uses this deep in the
bowels of distutils to decide what suffix to use when writing shared libraries
built by 'python setup.py build_ext'.
This means the patched Python only writes versioned .so files by default. I
personally don't see that as a problem, and it does not affect the test suite,
with the exception of one easily tweaked test. I don't know if third party
tools will care. The fact that traditional foo.so shared libraries will still
satisfy the import should be enough, I think.
The patch is currently Linux only, since I need this for Debian and Ubuntu and
wanted to keep the change narrow.
Other possible approaches:
* Extend the distutils API so that the .so file extension can be passed in,
instead of being essentially hardcoded to what Python's Makefile contains.
* Keep the dynload_shlib.c change, but modify the Debian/Ubuntu build
environment to pass in $SO to make (though the configure.in warning and
sleep is a little annoying).
* Add a ./configure option to enable this, which Debuntu's build would use.
The patch is available here:
and my working branch is here:
Please let me know what you think. I'm happy to just commit this to the py3k
branch if there are no objections <wink>. I don't think a new PEP is in
order, but an update to PEP 3147 might make sense.
While the EuroPython sprints are still going on, I am back home, and
after a somewhat restful night of sleep, I have some thoughts I'd like
to share before I get distracted. Note, I am jumping wildly between
- Commit privileges: Maybe we've been too careful with only giving
commit privileges to to experienced and trusted new developers. I
spoke to Ezio Melotti and from his experience with getting commit
privileges, it seems to be a case of "the lion is much more afraid of
you than you are afraid of the lion". I.e. having got privileges he
was very concerned about doing something wrong, worried about the
complexity of SVN, and so on. Since we've got lots of people watching
the commit stream, I think that there really shouldn't need to be a
worry at all about a new committer doing something malicious, and
there shouldn't be much worry about honest beginners' mistakes either
-- the main worry remains that new committers don't use their
privileges enough. So, my recommendation (which surely is a
turn-around of my *own* attitude in the past) is to give out more
commit privileges sooner.
- Concurrency and parallelism: Russel Winder and Sarah Mount pushed
the idea of CSP
several talks at the conference. They (at least Russell) emphasized
the difference between concurrency (interleaved event streams) and
parallelism (using many processors to speed things up). Their
prediction is that as machines with many processing cores become more
prevalent, the relevant architecture will change from cores sharing a
single coherent memory (the model on which threads are based) to one
where each core has a limited amount of private memory, and
communication is done via message passing between the cores. This
gives them (and me :-) hope that the GIL won't be a problem as long as
we adopt a parallel processing model. Two competing models are the
Actor model, which is based on asynchronous communication, and CSP,
which is synchronous (when a writer writes to a channel, it blocks
until a reader reads that value -- a rendezvous). At least Sarah
suggested that both models are important. She also mentioned that a
merger is under consideration between the two major CSP-for-Python
packages, Py-CSP and Python-CSP. I also believe that the merger will
be based on the stdlib multiprocessing package, but I'm not sure. I do
expect that we may get some suggestions from that corner to make some
minor changes to details of multiprocessing (and perhaps threading),
and I think we should be open to those (I expect these will be good
suggestions for small tweaks, not major overhauls).
- After seeing Raymond's talk about monocle (search for it on PyPI) I
am getting excited again about PEP 380 (yield from, return values from
generators). Having read the PEP on the plane back home I didn't see
anything wrong with it, so it could just be accepted in its current
form. Implementation will still have to wait for Python 3.3 because of
the moratorium. (Although I wouldn't mind making an exception to get
it into 3.2.)
- This made me think of how the PEP process should evolve so as to not
require my personal approval for every PEP. I think the model for
future PEPs should be the one we used for PEP 3148 (futures, which was
just approved by Jesse): the discussion is led and moderated by one
designated "PEP handler" (a different one for each PEP) and the PEP
handler, after reviewing the discussion, decides when the PEP is
approved. A PEP handler should be selected for each PEP as soon as
possible; without a PEP handler, discussing a PEP is not all that
useful. The PEP handler should be someone respected by the community
with an interest in the subject of the PEP but at an arms' length (at
least) from the PEP author. The PEP handler will have to moderate
feedback, separating useful comments from (too much) bikeshedding,
repetitious lines of questioning, and other forms of obstruction. The
PEP handler should also set and try to maintain a schedule for the
discussion. Note that a schedule should not be used to break a tie --
it should be used to stop bikeshedding and repeat discussions, while
giving all interested parties a chance to comment. (I should say that
this is probably similar to the role of an IETF working group director
with respect to RFCs.)
- Specifically, if Raymond is interested, I wouldn't mind seeing him
as the PEP handler for PEP 380. For some of Martin von Löwis's PEPs
(382, 384) I think a PEP handler is sorely lacking -- from the
language summit it appeared as if nobody besides Martin understands
- A lot of things seem to be happening to make PyPI better. Is this
being summarized somewhere? Based on some questions I received during
my keynote Q&A (http://bit.ly/bdflqa) I think not enough people are
aware of what we are already doing in this area. Frankly, I'm not sure
I do, either: I think I've heard of a GSOC student and of plans to
take over pypi.appspot.com (with the original developer's permission)
to become a full and up-to-date mirror. Mirroring apparently also
requires some client changes. Oh, and there's a proposed solution for
the "register user" problem where apparently the clients had been
broken by a unilateral change to the server to require a certain "yes
I agree" checkbox.
For a hopefully eventually exhaustive overview of what was
accomplished at EuroPython, go to http://wiki.europython.eu/After --
and if you know some blog about EuroPython not yet listed, please add
--Guido van Rossum (python.org/~guido)
I have two somewhat unrelated thoughts about PEPs.
* Accepted: header
When PEP 3147 was accepted, I had a few folks ask that this be recorded in the
PEP by including a link to the BDFL pronouncement email. I realized that
there's no formal way to express this in a PEP, and many PEPs in fact don't
record more than the fact that it was accepted. I'd like to propose
officially adding an Accepted: header which should include a URL to the email
or other web resource where the PEP is accepted. I've come as close as
possible to this (without modifying the supporting scripts or PEP 1) in PEP
I'd be willing to update things if there are no objections.
* EOL schedule for older releases.
We have semi-formal policies for the lifetimes of Python releases, though I'm
not sure this policy is written down in any of the existing informational
PEPs. However, we have release schedule PEPs going back to Python 1.6. It
seems reasonable to me that we include end-of-life information in those PEPs.
For example, we could state that Python 2.4 is no longer even being maintained
for security, and we could state the projected date that Python 2.6 will go
into security-only maintenance mode.
I would not mandate that we go back and update all previous PEPs for either of
these ideas. We'd adopt them moving forward and allow anyone who's motivated
to backfill information opportunistically.