python-peps/pep-0594.rst

PEP: 594
Title: Removing dead batteries from the standard library
Author: Christian Heimes <christian@python.org>
Discussions-To: https://discuss.python.org/t/pep-594-removing-dead-batteries-from-the-standard-library/1704
Status: Draft
Type: Standards Track
Content-Type: text/x-rst
Created: 20-May-2019
Post-History: 21-May-2019


Abstract
========

This PEP proposed a list of standard library modules to be removed from the
standard library. The modules are mostly historic data formats (e.g. Commodore
and SUN file formats), APIs and operating systems that have been superseded a
long time ago (e.g. Mac OS 9), or modules that have security implications and
better alternatives (e.g. password and login).

The PEP follows in the foot steps of other PEPS like :pep:`3108`. The
*Standard Library Reorganization* proposal removed a bunch of modules from
Python 3.0. In 2007, the PEP referred to maintenance burden as:

   "Over the years, certain modules have become a heavy burden upon python-dev
   to maintain. In situations like this, it is better for the module to be
   given to the community to maintain to free python-dev to focus more on
   language support and other modules in the standard library that do not take
   up an undue amount of time and effort."

The withdrawn :pep:`206` from 2000 expresses issues with the Python standard
library unvarnished and fortright:

   "[...] the standard library modules aren't always the best choices for a
   job. Some library modules were quick hacks (e.g. ``calendar``,
   ``commands``), some were designed poorly and are now near-impossible to
   fix (``cgi``), and some have been rendered obsolete by other, more complete
   modules [...]."


Rationale
=========

Back in the early days of Python, the interpreter came with a large set of
useful modules. This was often referred to as "batteries included"
philosophy and was one of the cornerstones to Python's success story.
Users didn't have to figure out how to download and install separate
packages in order to write a simple web server or parse email.

Times have changed. The introduction of the cheese shop (PyPI), setuptools,
and later pip, it became simple and straightforward to download and install
packages. Nowadays Python has a rich and vibrant ecosystem of third-party
packages. It's pretty much standard to either install packages from PyPI or
use one of the many Python or Linux distributions.

On the other hand, Python's standard library is piling up cruft, unnecessary
duplication of functionality, and dispensable features. This is undesirable
for several reasons.

* Any additional module increases the maintenance cost for the Python core
  development team. The team has limited resources, reduced maintenance cost
  frees development time for other improvements.
* Modules in the standard library are generally favored and seen as the
  de-facto solution for a problem. A majority of users only pick third-party
  modules to replace a stdlib module, when they have a compelling reason, e.g.
  ``lxml`` instead of ``xml``. The removal of an unmaintained stdlib module
  increases the chances of a community-contributed module to become widely
  used.
* A lean and mean standard library benefits platforms with limited resources
  like devices with just a few hundred kilobyte of storage (e.g. BBC
  Micro:bit). Python on mobile platforms like BeeWare or WebAssembly
  (e.g. pyodide) also benefit from reduced download size.

The modules in the PEP have been selected for deprecation because their
removal is either least controversial or most beneficial. For example,
least controversial are 30-year-old multimedia formats like the ``sunau``
audio format, which was used on SPARC and NeXT workstations in the late
1980s. The ``crypt`` module has fundamental flaws that are better solved
outside the standard library.

This PEP also designates some modules as not scheduled for removal. Some
modules have been deprecated for several releases or seem unnecessary at
first glance. However it is beneficial to keep the modules in the standard
library, mostly for environments where installing a package from PyPI is not
an option. This can be corporate environments or classrooms where external
code is not permitted without legal approval.

* The usage of FTP is declining, but some files are still provided over
  the FTP protocol or hosters offer FTP to upload content. Therefore
  ``ftplib`` is going to stay.
* The ``optparse`` and ``getopt`` modules are widely used. They are mature
  modules with very low maintenance overhead.
* According to David Beazley [5]_ the ``wave`` module is easy to teach to
  kids and can make crazy sounds. Making a computer generate crazy sounds is
  powerful and highly motivating exercise for a nine-year-old aspiring developer.
  It's a fun battery to keep.


Deprecation schedule
====================

3.8
---

This PEP targets Python 3.8. Version 3.8.0 final is scheduled to be released
a few months before Python 2.7 will reach its end of lifetime. We expect that
Python 3.8 will be targeted by users that migrate to Python 3 in 2019 and
2020. To reduce churn and to allow a smooth transition from Python 2,
Python 3.8 will neither raise ``DeprecationWarning`` nor remove any
modules that have been scheduled for removal. Instead deprecated modules will
just be *documented* as deprecated. Optionally modules may emit a
``PendingDeprecationWarning``.

All deprecated modules will also undergo a feature freeze. No additional
features should be added *unless* python-dev agrees that the deprecation of
the module is reverted and the code will not be removed. Bug should still be
fixed.

3.9
---

Starting with Python 3.9, deprecated modules will start issuing
``DeprecationWarning``. The `parser`_ module is removed and potentially
replaced with a new module.

All other deprecated modules are fully supported and will receive security
updates until Python 3.9 reaches its end-of-life. Python 3.9.0 will
be released about 18 months after 3.8.0 (April 2021?) and most likely
be supported for five years after the release. The estimated EOL of Python 3.9
is in 2026.

3.10
----

In 3.10 all deprecated modules will be removed from the CPython repository
together with tests, documentation, and autoconf rules.


PEP acceptance process
======================

3.8.0b1 is scheduled to be release shortly after the PEP is officially
submitted. Since it's improbable that the PEP will pass all stages of the
PEP process in time, I propose a two-step acceptance process that is
analogous to Python's two-release deprecation process.

The first *provisionally-accepted* phase targets Python 3.8.0b1. In the first
phase no code is changed or removed. Modules are only documented as
deprecated. The only exception is the `parser`_ module. It has been
documented as deprecated since Python 2.5 and is scheduled for removal for
3.9 to make place for a more advanced parser.

The final decision, which modules will be removed and how the removed code
is preserved, can be delayed for another year.


Deprecated modules
==================

The modules are grouped as data encoding, multimedia, network, OS interface,
and misc modules. The majority of modules are for old data formats or
old APIs. Some others are rarely useful and have better replacements on
PyPI, e.g. Pillow for image processing or NumPy-based projects to deal with
audio processing.

.. csv-table:: Table 1: Proposed modules deprecations
   :header: "Module", "Deprecated in", "To be removed", "Added in", "Has maintainer?", "Replacement"
   :widths: 2, 1, 1, 1, 1, 2

    aifc,3.8 (3.0\*),3.10,1993,**yes (inactive)**,\-
    asynchat,**3.6** (3.0\*),3.10,1999,**yes**,asyncio
    asyncore,**3.6** (3.0\*),3.10,1999,**yes**,asyncio
    audioop,3.8 (3.0\*),3.10,1992,**yes**,\-
    binhex,3.8,3.10,1995,no,\-
    cgi,3.8 (2.0\*\*),3.10,1995,no,\-
    cgitb,3.8 (2.0\*\*),3.10,1995,no,\-
    chunk,3.8,3.10,1999,no,\-
    crypt,3.8,3.10,1994,**yes (inactive)**,"legacycrypt, bcrypt, argon2cffi, hashlib, passlib"
    email.message.Message,3.3,3.10,2001,yes,email.message.EmailMessage
    email.mime,3.3,3.10,2001,yes,email.contentmanager
    email.policy.Compat32,3.3,3.10,2011,yes,email.policy.EmailPolicy
    formatter,**3.4**,3.10,1995,no,\-
    fpectl,**3.7**,**3.7**,1997,n/a,\-
    imghdr,3.8,3.10,1992,no,"filetype, puremagic, python-magic"
    imp,**3.4**,3.10,1990/1995,no,importlib
    macpath,**3.7**,**3.8**,1990,n/a,\-
    msilib,3.8,3.10,2006,no,\-
    nntplib,3.8,3.10,1992,no,\-
    nis,3.8 (3.0\*),3.10,1992,no,\-
    ossaudiodev,3.8,3.10,2002,no,\-
    parser,**2.5**,**3.9**,1993,**yes**,"ast, lib2to3.pgen2"
    pipes,3.8,3.10,1992,no,subprocess
    smtpd,"**3.4.7**, **3.5.4**",3.10,2001,**yes**,aiosmtpd
    sndhdr,3.8,3.10,1994,no,"filetype, puremagic, python-magic"
    spwd,3.8,3.10,2005,no,"python-pam, simplepam"
    sunau,3.8 (3.0\*),3.10,1993,no,\-
    telnetlib,3.8 (3.0\*),3.10,1997,no,"telnetlib3, Exscript"
    uu,3.8,3.10,1994,no,\-
    xdrlib,3.8,3.10,1992/1996,no,\-

Some module deprecations proposed by :pep:`3108` for 3.0 and :pep:`206` for
2.0. The *added in* column illustrates, when a module was originally designed
and added to the standard library. The *has maintainer* colum refers to the
`expert index <https://devguide.python.org/experts/>`_, a list of domain
experts and maintainers in the DevGuide.


Data encoding modules
---------------------

binhex
~~~~~~

The `binhex <https://docs.python.org/3/library/binhex.html>`_ module encodes
and decodes Apple Macintosh binhex4 data. It was originally developed for
TRS-80. In the 1980s and early 1990s it was used on classic Mac OS 9 to
encode binary email attachments.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

uu and the uu encoding
~~~~~~~~~~~~~~~~~~~~~~

The `uu <https://docs.python.org/3/library/uu.html>`_ module provides
uuencode format, an old binary encoding format for email from 1980. The uu
format has been replaced by MIME. The uu codec is provided by the ``binascii``
module.  There's also ``encodings/uu_codec.py`` which is a codec for the
same encoding; it should also be deprecated.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

xdrlib
~~~~~~

The `xdrlib <https://docs.python.org/3/library/xdrlib.html>`_ module supports
the Sun External Data Representation Standard. XDR is an old binary
serialization format from 1987. These days it's rarely used outside
specialized domains like NFS.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**


Multimedia modules
------------------

aifc
~~~~

The `aifc <https://docs.python.org/3/library/aifc.html>`_ module provides
support for reading and writing AIFF and AIFF-C files. The Audio Interchange
File Format is an old audio format from 1988 based on Amiga IFF. It was most
commonly used on the Apple Macintosh. These days only few specialized
application use AIFF.

A user disclosed [8]_ that the post production film industry makes heavy
use of the AIFC file format. The usage of the ``aifc`` module in closed source
and internal software was unknown prior to the first posting of this PEP. This
may be a compelling argument to keep the ``aifc`` module in the standard
library. The file format is stable and the module does not require much
maintenance. The strategic benefits for Python may outmatch the burden.

Module type
  pure Python (depends on some functions from `audioop`_ C extension)
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   yes, but expert is currently inactive.
Substitute
  **none**

audioop
~~~~~~~

The `audioop <https://docs.python.org/3/library/audioop.html>`_ module
contains helper functions to manipulate raw audio data and adaptive
differential pulse-code modulated audio data. The module is implemented in
C without any additional dependencies. The `aifc`_, `sunau`_, and `wave`_
modules depend on `audioop`_ for some operations.

The byteswap operation in the ``wave`` module can be substituted with little
extra work. In case ``aifc`` is not deprecated as well, a reduced version of
the ``audioop`` module is converted into a private implementation detail,
e.g. ``_audioop`` with ``byteswap``, ``alaw2lin``, ``ulaw2lin``, ``lin2alaw``,
``lin2ulaw``, and ``lin2adpcm``.

Module type
  C extension
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   yes
Substitute
  **none**

chunk
~~~~~

The `chunk <https://docs.python.org/3/library/chunk.html>`_ module provides
support for reading and writing Electronic Arts' Interchange File Format.
IFF is an old audio file format originally introduced for Commodore and
Amiga. The format is no longer relevant.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

imghdr
~~~~~~

The `imghdr <https://docs.python.org/3/library/imghdr.html>`_ module is a
simple tool to guess the image file format from the first 32 bytes
of a file or buffer. It supports only a limited number of formats and
neither returns resolution nor color depth.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  `puremagic <https://pypi.org/project/puremagic/>`_,
  `filetype <https://pypi.org/project/filetype/>`_,
  `python-magic <https://pypi.org/project/python-magic/>`_

ossaudiodev
~~~~~~~~~~~

The `ossaudiodev <https://docs.python.org/3/library/ossaudiodev.html>`_
module provides support for Open Sound System, an interface to sound
playback and capture devices. OSS was initially free software, but later
support for newer sound devices and improvements were proprietary. Linux
community abandoned OSS in favor of ALSA [1]_. Some operation systems like
OpenBSD and NetBSD provide an incomplete [2]_ emulation of OSS.

To best of my knowledge, FreeBSD is the only widespread operating system
that uses Open Sound System as of today. The ``ossaudiodev`` hasn't seen any
improvements or new features since 2003. All commits since 2003 are
project-wide code cleanups and a couple of bug fixes. It would be beneficial
for both FreeBSD community and core development, if the module would be
maintained and distributed by people that care for it and use it.

The standard library used to have more audio-related modules. The other
audio device interface (``audiodev``, ``linuxaudiodev``, ``sunaudiodev``)
were removed in 2007 as part of the :pep:`3108` stdlib re-organization.

Module type
  C extension
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

sndhdr
~~~~~~

The `sndhdr <https://docs.python.org/3/library/sndhdr.html>`_ module is
similar to the `imghdr`_ module but for audio formats. It guesses file
format, channels, frame rate, and sample widths from the first 512 bytes of
a file or buffer. The module only supports AU, AIFF, HCOM, VOC, WAV, and
other ancient formats.

Module type
  pure Python (depends on `audioop`_ C extension for some operations)
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  `puremagic <https://pypi.org/project/puremagic/>`_,
  `filetype <https://pypi.org/project/filetype/>`_,
  `python-magic <https://pypi.org/project/python-magic/>`_

sunau
~~~~~

The `sunau <https://docs.python.org/3/library/sunhdr.html>`_ module provides
support for Sun AU sound format. It's yet another old, obsolete file format.

Module type
  pure Python (depends on `audioop`_ C extension for some operations)
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**


Networking modules
------------------

asynchat
~~~~~~~~

The `asynchat <https://docs.python.org/3/library/asynchat.html>`_ module
is built on top of `asyncore`_ and has been deprecated since Python 3.6.

Module type
  pure Python
Deprecated in
  3.6
Removed in
  3.10
Has a designated expert
   yes
Substitute
  asyncio

asyncore
~~~~~~~~

The `asyncore <https://docs.python.org/3/library/asyncore.html>`_ module was
the first module for asynchronous socket service clients and servers. It
has been replaced by asyncio and is deprecated since Python 3.6.

The ``asyncore`` module is also used in stdlib tests. The tests for
``ftplib``, ``logging``, ``smptd``, ``smtplib``, and ``ssl`` are partly
based on ``asyncore``. These tests must be updated to use asyncio or
threading.

Module type
  pure Python
Deprecated in
  3.6
Removed in
  3.10
Has a designated expert
   yes
Substitute
  asyncio


cgi
~~~

The `cgi <https://docs.python.org/3/library/cgi.html>`_ module is a support
module for Common Gateway Interface (CGI) scripts. CGI is deemed as
inefficient because every incoming request is handled in a new process.
:pep:`206` considers the module as:

   "[...] designed poorly and are now near-impossible to fix (``cgi``) [...]"

Several people proposed to either keep the ``cgi`` module for features like
``cgi.parse_qs`` or move ``cgi.escape`` to a different module. The
functions ``cgi.parse_qs`` and ``cgi.parse_qsl`` have been
deprecated for a while and are actually aliases for
``urllib.parse.parse_qs`` and ``urllib.parse.parse_qsl``. The
function ``cgi.quote`` has been deprecated in favor of ``html.quote``
with secure default values.

Module type
  pure Python
Deprecated in
  3.8 (originally proposed for 2.0 by :pep:`206`)
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**


cgitb
~~~~~

The `cgitb <https://docs.python.org/3/library/cgitb.html>`_ module is a
helper for the ``cgi`` module for configurable tracebacks.

The ``cgitb`` module is not used by any major Python web framework (Django,
Pyramid, Plone, Flask, CherryPy, or Bottle). Only Paste uses it in an
optional debugging middleware.

Module type
  pure Python
Deprecated in
  3.8 (originally proposed for 2.0 by :pep:`206`)
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

email (legacy API)
~~~~~~~~~~~~~~~~~~

The `email <https://docs.python.org/3/library/email.html>`_ package is a
library for managing email messages. The email package contains several
legacy modules, legacy functions, and legacy classes, that provide backwards
compatibility to Python 3.2 and 2.7:

 * ``email.message.Message`` (replaced by ``email.message.EmailMessage``)
 * ``email.mime`` (replaced by ``email.contentmanager``)
 * ``email.header`` (replaced by dict-like API of ``EmailMessage`` class)
 * ``email.charset``
 * ``email.encoders`` (replaced by ``EmailMessage.set_content``)
 * ``email.utils`` (new API performs parsing and formatting automatically)
 * ``email.iterators``
 * ``email.policy.Compat32``

The classes ``email.mime.audio.MIMEAudio`` and ``email.mime.image.MIMEImage``
depend on the ``sndhdr`` and ``imghdr`` modules. In case the ``email.mime``
package is not removed, the auto-detection of file formats must be deprecated
and ``_subtype`` argument a required argument.

Module type
  pure Python
Deprecated in
  3.8 (documented as legacy APIs since 3.3 or 3.4)
To be removed in
  3.10
Has a designated expert
   yes
Substitute
  email (non-legacy APIs)

smtpd
~~~~~

The `smtpd <https://docs.python.org/3/library/smtpd.html>`_ module provides
a simple implementation of a SMTP mail server. The module documentation
marks the module as deprecated and recommends ``aiosmtpd`` instead. The
deprecation message was added in releases 3.4.7, 3.5.4, and 3.6.1.

Module type
  pure Python
Deprecated in
  **3.4.7**, **3.5.4**, **3.6.1**
To be removed in
  3.10
Has a designated expert
   yes
Substitute
  aiosmtpd

nntplib
~~~~~~~

The `nntplib <https://docs.python.org/3/library/nntplib.html>`_ module
implements the client side of the Network News Transfer Protocol (nntp). News
groups used to be a dominant platform for online discussions. Over the last
two decades, news has been slowly but steadily replaced with mailing lists
and web-based discussion platforms. Twisted is also
`planning <https://twistedmatrix.com/trac/ticket/9405>`_ to deprecate NNTP
support and `pynntp <https://github.com/greenbender/pynntp>`_ hasn't seen any
activity since 2014. This is a good indicator that the public interest in
NNTP support is declining.

The ``nntplib`` tests have been the cause of additional work in the recent
past. Python only contains client side of NNTP. The tests connect to
external news server. The servers are sometimes unavailable, too slow, or do
not work correctly over IPv6. The situation causes flaky test runs on
buildbots.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

telnetlib
~~~~~~~~~

The `telnetlib <https://docs.python.org/3/library/telnetlib.html>`_ module
provides a Telnet class that implements the Telnet protocol.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Substitute
  `telnetlib3 <https://pypi.org/project/telnetlib3>`_,
  `Exscript <https://pypi.org/project/Exscript/>`_


Operating system interface
--------------------------

crypt
~~~~~

The `crypt <https://docs.python.org/3/library/crypt.html>`_ module implements
password hashing based on the ``crypt(3)`` function from ``libcrypt`` or
``libxcrypt`` on Unix-like platforms. The algorithms are mostly old, of poor
quality and insecure. Users are discouraged to use them.

* The module is not available on Windows. Cross-platform applications need
  an alternative implementation anyway.
* Only DES encryption is guaranteed to be available. DES has an extremely
  limited key space of 2**56.
* MD5, salted SHA256, salted SHA512, and Blowfish are optional extensions.
  SSHA256 and SSHA512 are glibc extensions. Blowfish (bcrypt) is the only
  algorithm that is still secure. However it's in glibc and therefore not
  commonly available on Linux.
* Depending on the platform, the ``crypt`` module is not thread safe. Only
  implementations with ``crypt_r(3)`` are thread safe.
* The module was never useful to interact with system user and password
  databases. On BSD, macOS, and Linux, all user authentication and
  password modification operations must go through PAM (pluggable
  authentication module), see `spwd`_ deprecation.

Module type
  C extension + Python module
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   yes, but expert is currently inactive.
Substitute
  `legacycrypt <https://pypi.org/project/legacycrypt/>`_ (ctypes wrapper),
  `bcrypt <https://pypi.org/project/bcrypt/>`_,
  `passlib <https://pypi.org/project/passlib/>`_,
  `argon2cffi <https://pypi.org/project/argon2-cffi/>`_,
  hashlib module (PBKDF2, scrypt)

macpath
~~~~~~~

The `macpath <https://docs.python.org/3/library/macpath.html>`_ module
provides Mac OS 9 implementation of ``os.path`` routines. Mac OS 9 is no longer
supported.

Module type
  pure Python
Deprecated in
  3.7
Removed in
  3.8
Has a designated expert
   n/a
Substitute
  **none**

nis
~~~

The `nis <https://docs.python.org/3/library/nis.html>`_ module provides
NIS/YP support. Network Information Service / Yellow Pages is an old and
deprecated directory service protocol developed by Sun Microsystems. It's
designed successor NIS+ from 1992 never took off. For a long time, libc's
Name Service Switch, LDAP, and Kerberos/GSSAPI are considered a more powerful
and more secure replacement of NIS.

Module type
  C extension
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

spwd
~~~~

The `spwd <https://docs.python.org/3/library/spwd.html>`_ module provides
direct access to Unix shadow password database using non-standard APIs.

In general it's a bad idea to use spwd. It circumvents system
security policies, does not use the PAM stack, and is only compatible
with local user accounts, because it ignores NSS. The use of the ``spwd``
module for access control must be considered a *security bug*, as it bypasses
PAM's access control.

Further more the ``spwd`` module uses the
`shadow(3) <http://man7.org/linux/man-pages/man3/shadow.3.html>`_ APIs.
Functions like ``getspnam(3)`` access the ``/etc/shadow`` file directly. This
is dangerous and even forbidden for confined services on systems with a
security engine like SELinux or AppArmor.

Module type
  C extension
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  `python-pam <https://pypi.org/project/python-pam/>`_,
  `simpleplam <https://pypi.org/project/simplepam/>`_

Misc modules
------------

formatter
~~~~~~~~~

The `formatter <https://docs.python.org/3/library/formatter.html>`_ module
is an old text formatting module which has been deprecated since Python 3.4.

Module type
  pure Python
Deprecated in
  3.4
To be removed in
  3.10
Has a designated expert
   no
Substitute
  *n/a*

imp
~~~

The `imp <https://docs.python.org/3/library/imp.html>`_ module is the
predecessor of the
`importlib <https://docs.python.org/3/library/importlib.html>`_ module. Most
functions have been deprecated since Python 3.3 and the module since
Python 3.4.

Module type
  C extension
Deprecated in
  3.4
To be removed in
  3.10
Has a designated expert
   yes, experts have deprecated the module
Substitute
  importlib

msilib
~~~~~~

The `msilib <https://docs.python.org/3/library/msilib.html>`_ package is a
Windows-only package. It supports the creation of Microsoft Installers (MSI).
The package also exposes additional APIs to create cabinet files (CAB). The
module is used to facilitate distutils to create MSI installers with the
``bdist_msi`` command. In the past it was used to create CPython's official
Windows installer, too.

Microsoft is slowly moving away from MSI in favor of Windows 10 Apps (AppX)
as new deployment model [3]_.

Module type
  C extension + Python code
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  **none**

parser
~~~~~~

The `parser <https://docs.python.org/3/library/parser.html>`_ module provides
an interface to Python’s internal parser and bytecode compiler. The stdlib
has superior ways to interact with the parse tree. From Python 2.5 onward,
it's much more convenient to cut in at the Abstract Syntax Tree (AST)
generation and compilation stage.

The ``parser`` module causes additional work. It's C code that must be
kept in sync with any change to Python's grammar and internal parser.
Pablo wants to remove the parser module and promote lib2to3's pgen2 instead
[6]_.

Most importantly the presence of the ``parser`` module makes it harder to
switch to something more powerful than a LL(1) parser [7]_. Since the
``parser`` module is documented as deprecated since Python 2.5 and a new
parsing technology is planned for 3.9, the ``parser`` module is scheduled for
removal in 3.9.

Module type
  C extension
Deprecated in
  3.8, documented as deprecated since **2.5**
To be removed in
  **3.9**
Has a designated expert
   yes, experts have deprecated the module.
Substitute
  ast, lib2to3.pgen2

pipes
~~~~~

The `pipes <https://docs.python.org/3/library/pipes.html>`_ module provides
helpers to pipe the input of one command into the output of another command.
The module is built on top of ``os.popen``. Users are encouraged to use
the subprocess module instead.

Module type
  pure Python
Deprecated in
  3.8
To be removed in
  3.10
Has a designated expert
   no
Substitute
  subprocess module

Removed modules
===============

fpectl
------

The `fpectl <https://docs.python.org/3.6/library/fpectl.html>`_ module was
never built by default, its usage was discouraged and considered dangerous.
It also required a configure flag that caused an ABI incompatibility. The
module was removed in 3.7 by Nathaniel J. Smith in
`bpo-29137 <https://bugs.python.org/issue29137>`_.

Module type
  C extension + CAPI
Deprecated in
  3.7
Removed in
  3.7
Has a designated expert
   n/a
Substitute
  **none**


Modules to keep
===============

Some modules were originally proposed for deprecation.

.. csv-table:: Table 2: Withdrawn deprecations
   :header: "Module", "Deprecated in", "Replacement"
   :widths: 1, 1, 2

    colorsys,\-,"colormath, colour, colorspacious, Pillow"
    fileinput,\-,argparse
    getopt,\-,"argparse, optparse"
    lib2to3,\-,
    optparse,**3.2**,argparse
    wave,\-,

colorsys
--------

The `colorsys <https://docs.python.org/3/library/colorsys.html>`_ module
defines color conversion functions between RGB, YIQ, HSL, and HSV coordinate
systems.

Walter Dörwald, Petr Viktorin, and others requested to keep ``colorsys``. The
module is useful to convert CSS colors between coordinate systems. The
implementation is simple, mature, and does not impose maintenance overhead
on core development.

The PyPI packages ``colormath``, ``colour``, and ``colorspacious`` provide more and
advanced features. The Pillow library is better suited to transform images
between color systems.

Module type
  pure Python
Has a designated expert
   no
Substitute
  `colormath <https://pypi.org/project/colormath/>`_,
  `colour <https://pypi.org/project/colour/>`_
  `colorspacious <https://pypi.org/project/colorspacious/>`_,
  `Pillow <https://pypi.org/project/Pillow/>`_

fileinput
---------

The `fileinput <https://docs.python.org/3/library/fileinput.html>`_ module
implements helpers to iterate over a list of files from ``sys.argv``. The
module predates the ``optparser`` and ``argparser`` modules. The same functionality
can be implemented with the ``argparser`` module.

Several core developers expressed their interest to keep the module in the
standard library, as it is handy for quick scripts.

Module type
  pure Python
Has a designated expert
   no

lib2to3
-------

The `lib2to3 <https://docs.python.org/3/library/2to3.html>`_ package provides
the ``2to3`` command to transpile Python 2 code to Python 3 code.

The package is useful for other tasks besides porting code from Python 2 to
3. For example `Black`_ uses it for code reformatting.

Module type
  pure Python
Has a designated expert
   no

getopt
------

The `getopt <https://docs.python.org/3/library/getopt.html>`_ module mimics
C's ``getopt()`` option parser.

Although users are encouraged to use ``argparse`` instead, the ``getopt`` module is
still widely used. The module is small, simple, and handy for C developers
to write simple Python scripts.

Module type
  pure Python
Has a designated expert
   no
Substitute
  argparse

optparse
--------

The `optparse <https://docs.python.org/3/library/optparse.html>`_ module is
the predecessor of the ``argparse`` module.

Although it has been deprecated for many years, it's still too widely used
to remove it.

Module type
  pure Python
Deprecated in
  3.2
Has a designated expert
   yes
Substitute
  argparse

wave
----

The `wave <https://docs.python.org/3/library/wave.html>`_ module provides
support for the WAV sound format.

The module is not deprecated, because The WAV format is still relevant these
days. The ``wave`` module is also used in education, e.g. to show kids how
to make noise with a computer.

The module uses one simple function from the `audioop`_ module to perform
byte swapping between little and big endian formats. Before 24 bit WAV
support was added, byte swap used to be implemented with the ``array``
module. To remove ``wave``'s dependency on ``audioop``, the byte swap
function could be either be moved to another module (e.g. ``operator``) or
the ``array`` module could gain support for 24-bit (3-byte) arrays.

Module type
  pure Python (depends on *byteswap* from `audioop`_ C extension)
Has a designated expert
   no


Future maintenance of removed modules
=====================================

The main goal of the PEP is to reduce the burden and workload on the Python
core developer team. Therefore removed modules will not be maintained by
the core team as separate PyPI packages. However the removed code, tests and
documentation may be moved into a new Git repository, so community members
have a place from which they can pick up and fork code.

A first draft of a `legacylib <https://github.com/tiran/legacylib>`_
repository is available on my private GitHub account. The modules could be
made available on PyPI. The Python core team will not publish or maintain
the packages. It is my hope that members of the Python community will
adopt, maintain, and perhaps improve the deprecated modules.

It's my hope that some of the deprecated modules will be picked up and
adopted by users that actually care about them. For example ``colorsys`` and
``imghdr`` are useful modules, but have limited feature set. A fork of
``imghdr`` can add new features and support for more image formats, without
being constrained by Python's release cycle.

Most of the modules are in pure Python and can be easily packaged. Some
depend on a simple C module, e.g. `audioop`_ and `crypt`_. Since `audioop`_
does not depend on any external libraries, it can be shipped as binary
wheels with some effort. Other C modules can be replaced with ``ctypes`` or ``cffi``.
For example I created `legacycrypt`_, which provides a full implementation of
``crypt``. It is implemented on top of a ctypes wrapper around ``libxcrypt``
and ``libcrypt`` instead of a C extension like the original ``_crypt``
module.


Discussions
===========

* Elana Hashman and Nick Coghlan suggested to keep the ``getopt`` module.
* Berker Peksag proposed to deprecate and removed ``msilib``.
* Brett Cannon recommended to delay active deprecation warnings and removal
  of modules like ``imp`` until Python 3.10. Version 3.8 will be released
  shortly before Python 2 reaches end-of-life. A delay reduced churn for
  users that migrate from Python 2 to 3.8.
* Brett also came up with the idea to keep ``lib2to3``. The package is useful
  for other purposes, e.g. `Black <https://pypi.org/project/black/>`_ uses
  it to reformat Python code.
* At one point, distutils was mentioned in the same sentence as this PEP.
  To avoid lengthy discussion and delay of the PEP, I decided against dealing
  with distutils. Deprecation of the distutils package will be handled by
  another PEP.
* Multiple people (Gregory P. Smith, David Beazley, Nick Coghlan, ...)
  convinced me to keep the `wave`_ module. [4]_
* Gregory P. Smith proposed to deprecate `nntplib`_. [4]_
* Andrew Svetlov mentioned the ``socketserver`` module is questionable.
  However it's used to implement ``http.server`` and ``xmlrpc.server``. The
  stdlib doesn't have a replacement for the servers, yet.


Update history
==============

Update 1
--------

* Deprecate `parser`_ module
* Keep `fileinput`_ module
* Elaborate why ``crypt`` and ``spwd`` are dangerous and bad
* Improve sections for `cgitb`_, `colorsys`_, `nntplib`_, and `smtpd`_ modules
* The `colorsys`_, ``crypt``, `imghdr`_, `sndhdr`_, and ``spwd`` sections now
  list suitable substitutions
* Mention that ``socketserver`` is going to stay for ``http.server`` and
  ``xmlrpc.server``
* The future maintenance section now states that the deprecated modules
  may be adopted by Python community members

Update 2
--------

* Keep ``colorsys`` module
* Add experts
* Redirect discussions to discuss.python.org
* Deprecate `telnetlib`_
* Deprecate compat32 policy of email package
* Add creation year to overview table
* Mention :pep:`206` and :pep:`3108`
* Update sections for ``aifc``, ``audioop``, ``cgi``, and ``wave``.


References
==========

.. [1] https://en.wikipedia.org/wiki/Open_Sound_System#Free,_proprietary,_free
.. [2] https://man.openbsd.org/ossaudio
.. [3] https://blogs.msmvps.com/installsite/blog/2015/05/03/the-future-of-windows-installer-msi-in-the-light-of-windows-10-and-the-universal-windows-platform/
.. [4] https://twitter.com/ChristianHeimes/status/1130257799475335169
.. [5] https://twitter.com/dabeaz/status/1130278844479545351
.. [6] https://mail.python.org/pipermail/python-dev/2019-May/157464.html
.. [7] https://discuss.python.org/t/switch-pythons-parsing-tech-to-something-more-powerful-than-ll-1/379
.. [8] https://mail.python.org/pipermail/python-dev/2019-May/157634.html


Copyright
=========

This document has been placed in the public domain.



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