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:
http://code.google.com/p/googleappengine/issues/detail?id=671
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
threads?
--
--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:
PEP: 3145
Title: Asynchronous I/O For subprocess.Popen
Author: (James) Eric Pruitt, Charles R. McCreary, Josiah Carlson
Type: Standards Track
Content-Type: text/plain
Created: 04-Aug-2009
Python-Version: 3.2
Abstract:
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.
Motivation:
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 [1] [2] [3]. 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 [4] [5]. 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
process.
Rationale:
There is a documented need for asynchronous, non-blocking functionality in
subprocess.Popen [6] [7] [2] [3]. 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
file object.
Reference Implementation:
I have been maintaining a Google Code repository that contains all of my
changes including tests and documentation [9] as well as blog detailing
the problems I have come across in the development process [10].
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
platforms.
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
interval.
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.
References:
[1] [ python-Feature Requests-1191964 ] asynchronous Subprocess
http://mail.python.org/pipermail/python-bugs-list/2006-December/
036524.html
[2] Daily Life in an Ivory Basement : /feb-07/problems-with-subprocess
http://ivory.idyll.org/blog/feb-07/problems-with-subprocess
[3] How can I run an external command asynchronously from Python? - Stack
Overflow
http://stackoverflow.com/questions/636561/how-can-i-run-an-external-
command-asynchronously-from-python
[4] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation
http://docs.python.org/library/subprocess.html#subprocess.Popen.wait
[5] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation
http://docs.python.org/library/subprocess.html#subprocess.Popen.kill
[6] Issue 1191964: asynchronous Subprocess - Python tracker
http://bugs.python.org/issue1191964
[7] Module to allow Asynchronous subprocess use on Windows and Posix
platforms - ActiveState Code
http://code.activestate.com/recipes/440554/
[8] subprocess.rst - subprocdev - Project Hosting on Google Code
http://code.google.com/p/subprocdev/source/browse/doc/subprocess.rst?spec...
[9] subprocdev - Project Hosting on Google Code
http://code.google.com/p/subprocdev
[10] Python Subprocess Dev
http://subdev.blogspot.com/
Copyright:
This P.E.P. is licensed under the Open Publication License;
http://www.opencontent.org/openpub/.
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.
>
>
> --
> Regards,
> Benjamin
>
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.
cheer,
Georg
--
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.
Hello everyone.
I see several problems with the two hex-conversion function pairs that
Python offers:
1. binascii.hexlify and binascii.unhexlify
2. bytes.fromhex and bytes.hex
Problem #1:
bytes.hex is not implemented, although it was specified in PEP 358.
This means there is no symmetrical function to accompany bytes.fromhex.
Problem #2:
Both pairs perform the same function, although The Zen Of Python suggests
that
"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...
Problem #3:
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.
Problem #4:
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.
Problem #5:
binascii.hexlify returns a bytes type - although ideally, converting to hex
should
always return string types and converting from hex should always return
bytes.
IMO there is no meaning of bytes as an output of hexlify, since the output
is a
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
bytes
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
return bytes
hexlify (and bytes.hex) may receive bytes or strings and may only return
strings
Of course we may also consider a third option, which will allow the return
type of
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
option A.
To repeat problems #4 and #5, the current behavior does not match any
option:
* The return type of binascii.hexlify should be string, and this is not the
current behavior.
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
input)
#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 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
3147:
http://www.python.org/dev/peps/pep-3147/
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.
Thoughts?
-Barry
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Debugging a strange problem today, I got the following result:
Sockets open by stdlib libraries are open without the "keepalive"
option, so the system default is used. The system default under linux is
"no keepalive".
So, if you are using a URLlib connection, POP3 connection, IMAP
connection, etc., any stdlib that internally creates a socket, and your
server goes away suddendly (you lose network connectivity, by instance),
the library will wait FOREVER for the server. The client can't detect
that the server is not longer available.
The "keepalive" option will send a probe packed every X minutes of
inactivity, to check if the other side is still alive, even if the
connection is idle.
The issue is bad, but the solution is simple enough. Options:
1. All "client" libraries should create sockets with the "KEEPALIVE" option.
2. Modify the socket C module to create all sockets as "Keepalive" by
default.
3. To have a global variable in the socket module to change the default
for future sockets. Something like current "socket.setdefaulttimeout()".
The default should be "keepalive".
4. Modify client libraries to accept a new optional socket-like object
as an optional parameter. This would allow things like transparent
compression or encryption, or to replace the socket connection by
anything else (read/write to shared memory or database, for example).
This is an issue in Linux because by default the sockets are not
"keepalive". In other Unix systems, the default is "keepalive". I don't
know about MS Windows.
What do you think?. The solution seems trivial, after deciding the right
way to go.
PS: "socket.setdefaulttimeout()" is not enough, because it could
shutdown a perfectly functional connection, just because it was idle for
too long.
- --
Jesus Cea Avion _/_/ _/_/_/ _/_/_/
jcea(a)jcea.es - http://www.jcea.es/ _/_/ _/_/ _/_/ _/_/ _/_/
jabber / xmpp:jcea@jabber.org _/_/ _/_/ _/_/_/_/_/
. _/_/ _/_/ _/_/ _/_/ _/_/
"Things are not so easy" _/_/ _/_/ _/_/ _/_/ _/_/ _/_/
"My name is Dump, Core Dump" _/_/_/ _/_/_/ _/_/ _/_/
"El amor es poner tu felicidad en la felicidad de otro" - Leibniz
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We don't have any buildbot backing this system.
OSF/1 last version was in 1994, was picked by Digital (Tru64 Unix). Last
version of Tru64 was released in late 2006. Now Digital is owned by HP
with its own Unix (HP-UX).
Maybe we can drop OSF/1 safely supporting Tru64 yet, but we don't have
any buildbot running any of this systems...
Deprecated systems are documented in PEP-11.
- --
Jesus Cea Avion _/_/ _/_/_/ _/_/_/
jcea(a)jcea.es - http://www.jcea.es/ _/_/ _/_/ _/_/ _/_/ _/_/
jabber / xmpp:jcea@jabber.org _/_/ _/_/ _/_/_/_/_/
. _/_/ _/_/ _/_/ _/_/ _/_/
"Things are not so easy" _/_/ _/_/ _/_/ _/_/ _/_/ _/_/
"My name is Dump, Core Dump" _/_/_/ _/_/_/ _/_/ _/_/
"El amor es poner tu felicidad en la felicidad de otro" - Leibniz
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Does the online dev version of the docs build in response to docs
checkins, or just once a day?
(And is that written down somewhere and I've just forgotten where to
look...)
Cheers,
Nick.
--
Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia
---------------------------------------------------------------
I'm trying to get a good friend of mine to start doing bug triage on Python.
As part of my trying to mentor him on it, I've found that many of the common
things I do in triage, like setting a priority for priorityless bugs,
assigning them to people who obviously are the next step, requires enhanced
privileges.
He has no reputation in the Python community, so I'd be up for getting him
started on things that require fewer privileges like verifying older patches
still apply against newer Pythons, or maybe summarizing priority/assignment
changes to the list and having someone (possibly me) make the changes, etc...
However, I will step up for him and say that I've known him a decade, and he's
very trustworthy. He has been the president (we call that position Maximum
Leader) of our Linux Users Group here for 5 years or so.
Thoughts?
Thanks,
Sean
--
Sean Reifschneider, Member of Technical Staff <jafo(a)tummy.com>
tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability
At 10:59 AM 3/7/2010 -0800, Jeffrey Yasskin wrote:
>So is it that you just don't like the idea of blocking, and want to
>stop anything that relies on it from getting into the standard library?
Um, no. As I said before, call it a "parallel task queue" or
"parallel task manager" or something to that general effect and I'm on board.
It may not be in the Zen of Python, but ISTM that names should
generally follow use cases. It is something of a corollary to "one
obvious way to do it", in that if you see something whose name
matches what you want to do, then it should be obvious that that's
the way in question. ;-)
The use cases for "parallel task queues", however, are a subset of
those for "futures" in the general case. Since the proposed module
addresses most of the former but very little of the latter, calling
it futures is inappropriate.
Specifically, it's:
1. Confusing to people who don't know what futures are (see e.g R.D.
Murray's post), and
2. Underpowered for people who expect/want a more fully-featured
futures system along the lines of E or Deferreds.
It seems that the only people for whom it's an intuitively correct
description are people who've only had experience with more limited
futures models (like Java's). However, these people should not have
a problem understanding the notion of parallel task queueing or task
management, so changing the name isn't really a loss for them, and
it's a gain for everybody else.
> Given the set_result and set_exception methods, it's pretty
> straightforward to fill in the value of a future from something
> that isn't purely computational.
Those are described as "internal" methods in the PEP; by contrast,
the Deferred equivalents are part of the public API.
> Given a way to register "on-done" callbacks with the future, it
> would be straightforward to wait for a future without blocking, too.
Yes, and with a few more additions besides that one, you might be on
the way to an actual competitor for Deferreds. For example: retry
support, chaining, logging, API for transparent result processing,
coroutine support, co-ordination tools like locks, sempaphores and queues, etc.
These are all things you would very likely want or need if you
actually wanted to write a program using futures as *your main
computational model*, vs. just needing to toss out some parallel
tasks in a primarily synchronous program.
Of course, Deferreds are indeed overkill if all you're ever going to
want is a few parallel tasks, unless you're already skilled in using
Twisted or some wrapper for it.
So, I totally support having a simple task queue in the stdlib, as
there are definitely times I would've used such a thing for a quick
script, if it were available.
However, I've *also* had use cases for using futures as a
computational model, and so that's what I originally thought this PEP
was about. After the use cases were clarified, though, it seems to
me that *calling* it futures is a bad idea, because it's really just
a nice task queuing system.
I'm +1 on adding a nice task queuing system, -1 on calling it by any
other name. ;-)
