[issue16651] Find out what stdlib modules lack a pure Python implementation

[Raymond Hettinger]

Change by Raymond Hettinger :


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resolution:  -> out of date
stage:  -> resolved
status: open -> closed

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Change by Brett Cannon :


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nosy:  -brett.cannon

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Eric Snow]

Changes by Eric Snow :


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nosy: +superluser
versions: +Python 3.6 -Python 3.4

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Raymond Hettinger]

Raymond Hettinger added the comment:

I don't think itertools or collections.deque should go on this list.  The other 
implementations already have these and a pure python versions miss the point of 
these being high performance tools.  AFAICT, there is zero benefit to adding a 
bunch of extra code that will never get used.  It will only complicate my 
maintenance of those modules.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Tshepang Lekhonkhobe]

Changes by Tshepang Lekhonkhobe :


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nosy: +tshepang

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Ezio Melotti]

Changes by Ezio Melotti :


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dependencies: +Add OrderedDict written in C
nosy: +ezio.melotti
type:  -> enhancement

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Eric Snow]

Eric Snow added the comment:

Also missing a pure-Python implementation:

collections.defaultdict (relatively trivial)
collections.deque

In the spirit of what Brett said, I found that PyPy has an implementation 
already:

  https://bitbucket.org/pypy/pypy/src/default/lib_pypy/_collections.py

Jython and IronPython do not have pure Python implentations:
  http://hg.python.org/jython/file/default/src/org/python/modules/_collections
  http://ironpython.codeplex.com/SourceControl/changeset/view/99885#1091023

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

There is one additional benefit. I have already implemented audioop module in 
Python, and due to this it has found many bugs in the current C implementation 
(issue16686).

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

One thing I should say about this list of modules is please don't go nuts 
porting every single module blindly. There is always a possibility that another 
VM has already ported the code and has simply not contributed it back and so 
there is no need to write it from scratch and more just political wrangling to 
get contributions pushed upstream from other VMs. There might also be reasons 
to not worry about porting something. Always start a conversation first before 
starting a port; last thing I want is someone putting in the time to port some 
code that no one will necessarily use for a while.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I'm involved in both issues and I think it's good to have so much simple Python 
implementations as possible and to have C accelerators for any performance 
critical code.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Philip Jenvey]

Philip Jenvey added the comment:

The guidelines for this are in PEP 399. Basically, adding 'accelerated' 
implementations when necessary isn't a bad thing as long as there are pure 
Python equivalents (unless it's a special case) and both are tested.

issue14373's latest patch seems to be following the PEP

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Meador Inge]

Meador Inge added the comment:

I noticed functools in the list.  issue14373 was opened somewhat recently to 
reimplement functools.lru_cache in C.  This issue seems to be promoting have 
more things implemented in pure Python.  Someone involved in this issue might 
want to weigh in on issue14373 if that is the case.

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nosy: +meador.inge

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Éric Araujo]

Éric Araujo added the comment:

Oops, sorry I slipped :)

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


--
dependencies: +Add pure Python operator module

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Philip Jenvey]

Philip Jenvey added the comment:

PyPy had a pure python itertools until recently (it's been deleted):

https://bitbucket.org/pypy/pypy/src/c1aa74c06e86/lib_pypy/itertools.py?at=py3k

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Terry J. Reedy]

Terry J. Reedy added the comment:

itertools should be fairly easy as the docs already contain Python equivalents 
(or near equivalents).

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Zachary Ware]

Changes by Zachary Ware :


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nosy: +zach.ware

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

Eric, I know you didn't just mean to suggest Python != efficient. =)

Yes, it should be in the list because other VMs might not want to re-implement 
that code in some native language to the VM. And I assume all code in the 
stdlib tries to be efficient, so that label holds no sway with me.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Éric Araujo]

Éric Araujo added the comment:

Should itertools be in the list, as its stated purpose is to provide highly 
efficient functions?

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

Alex: yes, the builtins could almost all be re-implemented in pure Python, but 
there is a performance consideration vs. benefit (e.g. if we re-implemented 
map() in Python which VMs would use it vs. implement it in some native way for 
performance?).

But one place I think there could be a benefit w/o performance issues is the 
built-in exceptions as you should be able to store references to the classes to 
help minimize the added cost of startup creating the exceptions from Python 
code.

Amaury: other VMs and easier extensibility in the future. We might as well all 
share the burden of maintaining pure Python versions instead of re-implementing 
the same thing over and over in little VM silos. And if some new thing needs to 
be added for a module it's easier to do it in Python than C (which then also 
continues to benefit other VMs).

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

What's the purpose of these alternate implementations?  For education, 
experiments?  As a replacement for other VMs?

Other modules that could be considered:
marshal
operator
unicodedata

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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dependencies: +Pure Python implementation of random

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Alex Gaynor]

Alex Gaynor added the comment:

A lot of builtins :)

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

Sure, a general XML parsing library could be written in Python, but they 
wouldn't be named expat. =) The expat module wraps a specific XML parser 
(expat) so I still do not consider it applicable for this list.

As for random, you are right that it doesn't use platform-specific random code.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

> So expat doesn't count as that literally wraps the expat library.

XML parser can be implemented in pure Python. There are a lot of XML parsers 
implemented in different programming languages.

> Random
> also requires accessing the system randomization libraries to work
> properly so I don't think that is a candidate either.

No, random have C implemented some basic methods only for speed. It uses 
time() system function for initial seeding, but time() is accessible from pure 
Python too.

Some OS-specific modules (pwd, grp, spwd, resource, ossaudiodev, etc) can be 
implemented in pure Python on some platforms (using I/O and ioctl on special 
files in /etc, /dev or /proc).

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brian Curtin]

Brian Curtin added the comment:

winreg does not have a pure equivalent, nor could it

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nosy: +brian.curtin

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Philip Jenvey]

Philip Jenvey added the comment:

zipimport

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Antoine Pitrou]

Antoine Pitrou added the comment:

Agreed with Brett.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

No, sqlite does not belong on this list as it wraps a C library. Plus there is 
an explicit block for ctypes-based modules in the stdlib which would prevent 
moving over the PyPy implementation.

And I'm sure pure Python versions of all the crypto libraries are out there, 
but I would be worried about them being implemented wrong, too slow to care, 
etc. Plus short of PyPy all of the other VMs have access to those crypto 
libraries in their own standard library so there is no need to provide it in 
Python's in pure Python.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Christian Heimes]

Christian Heimes added the comment:

All cryptographic hash function are available as pure Python implementations. 
Although the Python based variants are super slow (except maybe on PyPy), they 
still serve as an academic show case.

IIRC PyPy has pure Python implementations of MD5, SHA-1 and SHA-2 family.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc added the comment:

PyPy has a pure Python implementation of sqlite (using ctypes):
https://bitbucket.org/pypy/pypy/src/default/lib_pypy/_sqlite3.py

It most probably works on CPython as well.
Does it belong to this list?

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nosy: +amaury.forgeotdarc

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Arfrever Frehtes Taifersar Arahesis]

Changes by Arfrever Frehtes Taifersar Arahesis :


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nosy: +Arfrever

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

Brett Cannon added the comment:

So expat doesn't count as that literally wraps the expat library. Random also 
requires accessing the system randomization libraries to work properly so I 
don't think that is a candidate either. As for the compression libraries, those 
could be re-implemented, but I view those as wrappers around the libraries 
(same as the crypto stuff). I mean it doesn't have to be that way, but I'm 
trying to keep this framed in a tractable problem to start.

So to summarize the non-contentious modules (including adding functools) in 
alphabetical order, that puts us at:

array
audioop
binascii
cjkcodecs
csv
functools
itertools
re
struct

I would be curious to see what frequency these modules are used to know what 
might be higher priority so that the least used modules could eventually be 
marked as CPython-specific.

And to answer Chris' question, there is no need to be able to generate this 
from the docs until there is some PEP listing what modules must be implemented 
by a VM in order to considers its stdlib complete.

And thanks for the help so far, everyone!

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Chris Jerdonek]

Chris Jerdonek added the comment:

Would it make sense for this list to be somehow reflected in or be 
reconstructible from the documentation?

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Andrew Svetlov]

Changes by Andrew Svetlov :


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nosy: +asvetlov

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Christian Heimes]

Christian Heimes added the comment:

hashlib backends (md5, sha1, sha256 / 384 / 512) either through openssl 
wrappers or implementations based on libtomcrypt.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Alex Gaynor]

Changes by Alex Gaynor :


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nosy: +alex

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

array
audioop
binascii
random
re
struct
xml.parsers.expat
cjkcodecs

zlib, bz2, lzma and crypts also can be implemented in pure Python.

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[issue16651] Find out what stdlib modules lack a pure Python implementation

[Brett Cannon]

New submission from Brett Cannon:

I'm wondering which modules in the stdlib lack pure Python implementations (and 
could legitimately have one, e.g. sqlite can't really have a pure Python 
implementation). Once we know how big/small the list is a decision could be 
made as to whether to take on the effort to bring over some pure Python version 
from another VM or something for any of these modules.

To start the list:

csv
itertools

--
components: Library (Lib)
keywords: easy
messages: 177230
nosy: brett.cannon
priority: low
severity: normal
status: open
title: Find out what stdlib modules lack a pure Python implementation
versions: Python 3.4

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