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Python Enhancement Proposals

PEP 594 – Removing dead batteries from the standard library

Author
Christian Heimes <christian at python.org>, Brett Cannon <brett at python.org>
Discussions-To
Discourse thread
Status
Accepted
Type
Standards Track
Created
20-May-2019
Python-Version
3.11
Post-History
21-May-2019, 04-Feb-2022
Resolution
Discourse post

Table of Contents

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 footsteps 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The withdrawn PEP 206 from 2000 expresses issues with the Python standard library in an unvarnished and forthright manner:

“[…] 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. With the introduction of PyPI (née Cheeseshop), 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 with 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 this 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 sounds is a powerful and highly motivating exercise for a nine-year-old aspiring developer. It’s a fun battery to keep.

Deprecation schedule

3.11

Starting with Python 3.11, deprecated modules will start issuing DeprecationWarning. The estimated EOL of Python 3.10, the last version without the warning, is October 2026.

3.12

There should be no specific change compared to Python 3.11. This is the last version of Python with the deprecated modules, with an estimated EOL of October 2028.

3.13

All modules deprecated by this PEP are removed from the main branch of the CPython repository and are no longer distributed as part of Python.

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.

Table 1: Proposed modules deprecations
Module Deprecated in To be removed Added in Has maintainer? Replacement
aifc 3.11 (3.0*) 3.13 1993 yes (inactive) -
asynchat 3.6 (3.0*) 3.12 1999 yes asyncio
asyncore 3.6 (3.0*) 3.12 1999 yes asyncio
audioop 3.11 (3.0*) 3.13 1992 yes -
cgi 3.11 (2.0**) 3.13 1995 no -
cgitb 3.11 (2.0**) 3.13 1995 no -
chunk 3.11 3.13 1999 no -
crypt 3.11 3.13 1994 yes (inactive) legacycrypt, bcrypt, argon2-cffi, hashlib, passlib
imghdr 3.11 3.13 1992 no filetype, puremagic, python-magic
mailcap 3.11 3.13 1995 no -
msilib 3.11 3.13 2006 no -
nntplib 3.11 3.13 1992 no -
nis 3.11 (3.0*) 3.13 1992 no -
ossaudiodev 3.11 3.13 2002 no -
pipes 3.11 3.13 1992 no subprocess
smtpd 3.4.7, 3.5.4 3.12 2001 yes aiosmtpd
sndhdr 3.11 3.13 1994 no filetype, puremagic, python-magic
spwd 3.11 3.13 2005 no python-pam
sunau 3.11 (3.0*) 3.13 1993 no -
telnetlib 3.11 (3.0*) 3.13 1997 no telnetlib3, Exscript
uu 3.11 3.13 1994 no -
xdrlib 3.11 3.13 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 column refers to the expert index, a list of domain experts and maintainers in the DevGuide.

Data encoding modules

uu and the uu encoding

The uu 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.

xdrlib

The xdrlib 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.

Multimedia modules

aifc

The aifc 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 [6] 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.

audioop

The audioop 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.

chunk

The chunk 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.

imghdr

The imghdr 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.

ossaudiodev

The ossaudiodev 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 operating 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 interfaces (audiodev, linuxaudiodev, sunaudiodev) were removed in 2007 as part of the PEP 3108 stdlib re-organization.

sndhdr

The sndhdr 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.

sunau

The sunau module provides support for Sun AU sound format. It’s yet another old, obsolete file format.

Networking modules

asynchat

The asynchat module is built on top of asyncore and has been deprecated since Python 3.6.

asyncore

The asyncore 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.

cgi

The cgi 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) […]”

Replacements for the various parts of cgi which are not directly related to executing code are:

  • parse with urllib.parse.parse_qs (parse is just a wrapper)
  • parse_header with email.message.Message (see example below)
  • parse_multipart with email.message.Message (same MIME RFCs)
  • FieldStorage/MiniFieldStorage has no direct replacement, but can typically be replaced by using multipart (for POST and PUT requests) or urllib.parse.parse_qsl (for GET and HEAD requests)
  • valid_boundary (undocumented) with re.compile("^[ -~]{0,200}[!-~]$")

As an explicit example of how close parse_header and email.message.Message are:

>>> from cgi import parse_header
>>> from email.message import Message
>>> parse_header(h)
('application/json', {'charset': 'utf8'})
>>> m = Message()
>>> m['content-type'] = h
>>> m.get_params()
[('application/json', ''), ('charset', 'utf8')]
>>> m.get_param('charset')
'utf8'

cgitb

The cgitb 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.

smtpd

The smtpd 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.

nntplib

The nntplib 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 to deprecate NNTP support and 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 the client side of NNTP, so the tests connect to external news servers. The servers are sometimes unavailable, too slow, or do not work correctly over IPv6. The situation causes flaky test runs on buildbots.

telnetlib

The telnetlib module provides a Telnet class that implements the Telnet protocol.

Operating system interface

crypt

The crypt 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 from using 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 the spwd deprecation.

nis

The nis module provides NIS/YP support. Network Information Service / Yellow Pages is an old and deprecated directory service protocol developed by Sun Microsystems. Its designed successor NIS+ from 1992 never took off. For a long time, libc’s Name Service Switch, LDAP, and Kerberos/GSSAPI have been considered a more powerful and more secure replacement for NIS.

spwd

The spwd 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.

Furthermore, the spwd module uses the shadow(3) 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.

Misc modules

mailcap

The mailcap package reads mail capability files to assist in handling a file attachment in an email. In most modern operating systems the email client itself handles reacting to file attachments. Operating systems also have their own way to register handling files by their file name extension. Finally, the module has CVE-2015-20107 filed against it while having no maintainer to help fix it.

msilib

The msilib 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 a new deployment model [3].

pipes

The pipes 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.

Modules to keep

Some modules were originally proposed for deprecation but are no longer listed as such in this PEP.

Table 2: Withdrawn deprecations
Module Deprecated in Replacement
colorsys - colormath, colour, colorspacious, Pillow
fileinput - argparse
getopt - argparse, optparse
optparse 3.2 argparse
wave -

colorsys

The colorsys 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.

fileinput

The fileinput module implements helpers to iterate over a list of files from sys.argv. The module predates the optparse and argparse modules. The same functionality can be implemented with the argparse module.

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

getopt

The getopt 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.

optparse

The optparse 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.

wave

The wave 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.

Discussions

  • Elana Hashman and Nick Coghlan suggested to keep the getopt module.
  • Berker Peksag proposed to deprecate and remove 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.
  • 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.

Rejected ideas

Creating/maintaining a separate repo for the deprecated modules

It was previously proposed to create a separate repository containing the deprecated modules packaged for installation. One of the PEP authors went so far as to create a demo repository. In the end, though, it was decided that the added workload to create and maintain such a repo officially wasn’t justified, as the source code will continue to be available in the CPython repository for people to vendor as necessary. Similar work has also not been done when previous modules were deprecated and removed, and it seemingly wasn’t an undue burden on the community.

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.

Update 3

  • Keep the legacy email API modules. Internal deprecations will be handled separately.

Update 4

  • Add Brett as a co-author.
  • Retarget the PEP for Python 3.11.
  • Examples of how to replace the relevant parts of cgi (thanks Martijn Pieters).

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] (1, 2)
https://twitter.com/ChristianHeimes/status/1130257799475335169
[5]
https://twitter.com/dabeaz/status/1130278844479545351
[6]
https://mail.python.org/pipermail/python-dev/2019-May/157634.html

Source: https://github.com/python/peps/blob/main/pep-0594.rst

Last modified: 2022-04-26 19:10:00 GMT