# History and License

## History of the software

Python was created in the early 1990s by Guido van Rossum at Stichting Mathematisch Centrum (CWI, see https://www.cwi.nl) in the Netherlands as a successor of a language called ABC. Guido remains Python’s principal author, although it includes many contributions from others.

In 1995, Guido continued his work on Python at the Corporation for National Research Initiatives (CNRI, see https://www.cnri.reston.va.us) in Reston, Virginia where he released several versions of the software.

In May 2000, Guido and the Python core development team moved to BeOpen.com to form the BeOpen PythonLabs team. In October of the same year, the PythonLabs team moved to Digital Creations, which became Zope Corporation. In 2001, the Python Software Foundation (PSF, see https://www.python.org/psf/) was formed, a non-profit organization created specifically to own Python-related Intellectual Property. Zope Corporation was a sponsoring member of the PSF.

All Python releases are Open Source (see https://opensource.org for the Open Source Definition). Historically, most, but not all, Python releases have also been GPL-compatible; the table below summarizes the various releases.

Release | Derived from | Year | Owner | GPL-compatible? (1)
--- | --- | --- | --- | ---
0.9.0 thru 1.2 | n/a | 1991-1995 | CWI | yes
1.3 thru 1.5.2 | 1.2 | 1995-1999 | CNRI | yes
1.6 | 1.5.2 | 2000 | CNRI | no
2.0 | 1.6 | 2000 | BeOpen.com | no
1.6.1 | 1.6 | 2001 | CNRI | yes (2)
2.1 | 2.0+1.6.1 | 2001 | PSF | no
2.0.1 | 2.0+1.6.1 | 2001 | PSF | yes
2.1.1 | 2.1+2.0.1 | 2001 | PSF | yes
2.1.2 | 2.1.1 | 2002 | PSF | yes
2.1.3 | 2.1.2 | 2002 | PSF | yes
2.2 and above | 2.1.1 | 2001-now | PSF | yes

Note

1. GPL-compatible doesn’t mean that we’re distributing Python under the GPL. All Python licenses, unlike the GPL, let you distribute a modified version without making your changes open source. The GPL-compatible licenses make it possible to combine Python with other software that is released under the GPL; the others don’t.

2. According to Richard Stallman, 1.6.1 is not GPL-compatible, because its license has a choice of law clause. According to CNRI, however, Stallman’s lawyer has told CNRI’s lawyer that 1.6.1 is “not incompatible” with the GPL.

Thanks to the many outside volunteers who have worked under Guido’s direction to make these releases possible.

## Terms and conditions for accessing or otherwise using Python

Python software and documentation are licensed under the Python Software Foundation License Version 2.

Starting with Python 3.8.6, examples, recipes, and other code in the documentation are dual licensed under the PSF License Version 2 and the Zero-Clause BSD license.

Some software incorporated into Python is under different licenses. The licenses are listed with code falling under that license. See Licenses and Acknowledgements for Incorporated Software for an incomplete list of these licenses.

### PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2

    1. This LICENSE AGREEMENT is between the Python Software Foundation ("PSF"), and
       the Individual or Organization ("Licensee") accessing and otherwise using this
       software ("Python") in source or binary form and its associated documentation.

    2. Subject to the terms and conditions of this License Agreement, PSF hereby
       grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
       analyze, test, perform and/or display publicly, prepare derivative works,
       distribute, and otherwise use Python alone or in any derivative
       version, provided, however, that PSF's License Agreement and PSF's notice of
       copyright, i.e., "Copyright © 2001-2024 Python Software Foundation; All Rights
       Reserved" are retained in Python alone or in any derivative version
       prepared by Licensee.

    3. In the event Licensee prepares a derivative work that is based on or
       incorporates Python or any part thereof, and wants to make the
       derivative work available to others as provided herein, then Licensee hereby
       agrees to include in any such work a brief summary of the changes made to Python.

    4. PSF is making Python available to Licensee on an "AS IS" basis.
       PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF
       EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND DISCLAIMS ANY REPRESENTATION OR
       WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE
       USE OF PYTHON WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

    5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON
       FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF
       MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON, OR ANY DERIVATIVE
       THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.

    6. This License Agreement will automatically terminate upon a material breach of
       its terms and conditions.

    7. Nothing in this License Agreement shall be deemed to create any relationship
       of agency, partnership, or joint venture between PSF and Licensee.  This License
       Agreement does not grant permission to use PSF trademarks or trade name in a
       trademark sense to endorse or promote products or services of Licensee, or any
       third party.

    8. By copying, installing or otherwise using Python, Licensee agrees
       to be bound by the terms and conditions of this License Agreement.

### BEOPEN.COM LICENSE AGREEMENT FOR PYTHON 2.0

BEOPEN PYTHON OPEN SOURCE LICENSE AGREEMENT VERSION 1

    1. This LICENSE AGREEMENT is between BeOpen.com ("BeOpen"), having an office at
       160 Saratoga Avenue, Santa Clara, CA 95051, and the Individual or Organization
       ("Licensee") accessing and otherwise using this software in source or binary
       form and its associated documentation ("the Software").

    2. Subject to the terms and conditions of this BeOpen Python License Agreement,
       BeOpen hereby grants Licensee a non-exclusive, royalty-free, world-wide license
       to reproduce, analyze, test, perform and/or display publicly, prepare derivative
       works, distribute, and otherwise use the Software alone or in any derivative
       version, provided, however, that the BeOpen Python License is retained in the
       Software, alone or in any derivative version prepared by Licensee.

    3. BeOpen is making the Software available to Licensee on an "AS IS" basis.
       BEOPEN MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF
       EXAMPLE, BUT NOT LIMITATION, BEOPEN MAKES NO AND DISCLAIMS ANY REPRESENTATION OR
       WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE
       USE OF THE SOFTWARE WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

    4. BEOPEN SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF THE SOFTWARE FOR
       ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF USING,
       MODIFYING OR DISTRIBUTING THE SOFTWARE, OR ANY DERIVATIVE THEREOF, EVEN IF
       ADVISED OF THE POSSIBILITY THEREOF.

    5. This License Agreement will automatically terminate upon a material breach of
       its terms and conditions.

    6. This License Agreement shall be governed by and interpreted in all respects
       by the law of the State of California, excluding conflict of law provisions.
       Nothing in this License Agreement shall be deemed to create any relationship of
       agency, partnership, or joint venture between BeOpen and Licensee.  This License
       Agreement does not grant permission to use BeOpen trademarks or trade names in a
       trademark sense to endorse or promote products or services of Licensee, or any
       third party.  As an exception, the "BeOpen Python" logos available at
       http://www.pythonlabs.com/logos.html may be used according to the permissions
       granted on that web page.

    7. By copying, installing or otherwise using the software, Licensee agrees to be
       bound by the terms and conditions of this License Agreement.

### CNRI LICENSE AGREEMENT FOR PYTHON 1.6.1

    1. This LICENSE AGREEMENT is between the Corporation for National Research
       Initiatives, having an office at 1895 Preston White Drive, Reston, VA 20191
       ("CNRI"), and the Individual or Organization ("Licensee") accessing and
       otherwise using Python 1.6.1 software in source or binary form and its
       associated documentation.

    2. Subject to the terms and conditions of this License Agreement, CNRI hereby
       grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
       analyze, test, perform and/or display publicly, prepare derivative works,
       distribute, and otherwise use Python 1.6.1 alone or in any derivative version,
       provided, however, that CNRI's License Agreement and CNRI's notice of copyright,
       i.e., "Copyright © 1995-2001 Corporation for National Research Initiatives; All
       Rights Reserved" are retained in Python 1.6.1 alone or in any derivative version
       prepared by Licensee.  Alternately, in lieu of CNRI's License Agreement,
       Licensee may substitute the following text (omitting the quotes): "Python 1.6.1
       is made available subject to the terms and conditions in CNRI's License
       Agreement.  This Agreement together with Python 1.6.1 may be located on the
       internet using the following unique, persistent identifier (known as a handle):
       1895.22/1013.  This Agreement may also be obtained from a proxy server on the
       internet using the following URL: http://hdl.handle.net/1895.22/1013".

    3. In the event Licensee prepares a derivative work that is based on or
       incorporates Python 1.6.1 or any part thereof, and wants to make the derivative
       work available to others as provided herein, then Licensee hereby agrees to
       include in any such work a brief summary of the changes made to Python 1.6.1.

    4. CNRI is making Python 1.6.1 available to Licensee on an "AS IS" basis.  CNRI
       MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED.  BY WAY OF EXAMPLE,
       BUT NOT LIMITATION, CNRI MAKES NO AND DISCLAIMS ANY REPRESENTATION OR WARRANTY
       OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF
       PYTHON 1.6.1 WILL NOT INFRINGE ANY THIRD PARTY RIGHTS.

    5. CNRI SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON 1.6.1 FOR
       ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF
       MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON 1.6.1, OR ANY DERIVATIVE
       THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.

    6. This License Agreement will automatically terminate upon a material breach of
       its terms and conditions.

    7. This License Agreement shall be governed by the federal intellectual property
       law of the United States, including without limitation the federal copyright
       law, and, to the extent such U.S. federal law does not apply, by the law of the
       Commonwealth of Virginia, excluding Virginia's conflict of law provisions.
       Notwithstanding the foregoing, with regard to derivative works based on Python
       1.6.1 that incorporate non-separable material that was previously distributed
       under the GNU General Public License (GPL), the law of the Commonwealth of
       Virginia shall govern this License Agreement only as to issues arising under or
       with respect to Paragraphs 4, 5, and 7 of this License Agreement.  Nothing in
       this License Agreement shall be deemed to create any relationship of agency,
       partnership, or joint venture between CNRI and Licensee.  This License Agreement
       does not grant permission to use CNRI trademarks or trade name in a trademark
       sense to endorse or promote products or services of Licensee, or any third
       party.

    8. By clicking on the "ACCEPT" button where indicated, or by copying, installing
       or otherwise using Python 1.6.1, Licensee agrees to be bound by the terms and
       conditions of this License Agreement.

### CWI LICENSE AGREEMENT FOR PYTHON 0.9.0 THROUGH 1.2

    Copyright © 1991 - 1995, Stichting Mathematisch Centrum Amsterdam, The
    Netherlands.  All rights reserved.

    Permission to use, copy, modify, and distribute this software and its
    documentation for any purpose and without fee is hereby granted, provided that
    the above copyright notice appear in all copies and that both that copyright
    notice and this permission notice appear in supporting documentation, and that
    the name of Stichting Mathematisch Centrum or CWI not be used in advertising or
    publicity pertaining to distribution of the software without specific, written
    prior permission.

    STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
    SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
    EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE FOR ANY SPECIAL, INDIRECT
    OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
    DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
    ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
    SOFTWARE.

### ZERO-CLAUSE BSD LICENSE FOR CODE IN THE PYTHON DOCUMENTATION

    Permission to use, copy, modify, and/or distribute this software for any
    purpose with or without fee is hereby granted.

    THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
    REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
    AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
    INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
    LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
    OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
    PERFORMANCE OF THIS SOFTWARE.

## Licenses and Acknowledgements for Incorporated Software

This section is an incomplete, but growing list of licenses and acknowledgements for third-party software incorporated in the Python distribution.

### Mersenne Twister

The `_random` C extension underlying the `random` module includes code based on a download from http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/emt19937ar.html. The following are the verbatim comments from the original code:

    A C-program for MT19937, with initialization improved 2002/1/26.
    Coded by Takuji Nishimura and Makoto Matsumoto.

    Before using, initialize the state by using init_genrand(seed)
    or init_by_array(init_key, key_length).

    Copyright (C) 1997 - 2002, Makoto Matsumoto and Takuji Nishimura,
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.

     3. The names of its contributors may not be used to endorse or promote
        products derived from this software without specific prior written
        permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
    CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
    EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
    LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
    NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
    SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    Any feedback is very welcome.
    http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
    email: m-mat @ math.sci.hiroshima-u.ac.jp (remove space)

### Sockets

The `socket` module uses the functions, `getaddrinfo()`, and `getnameinfo()`, which are coded in separate source files from the WIDE Project, https://www.wide.ad.jp/.

    Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.
    3. Neither the name of the project nor the names of its contributors
       may be used to endorse or promote products derived from this software
       without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

### Asynchronous socket services

The `test.support.asynchat` and `test.support.asyncore` modules contain the following notice:

    Copyright 1996 by Sam Rushing

                            All Rights Reserved

    Permission to use, copy, modify, and distribute this software and
    its documentation for any purpose and without fee is hereby
    granted, provided that the above copyright notice appear in all
    copies and that both that copyright notice and this permission
    notice appear in supporting documentation, and that the name of Sam
    Rushing not be used in advertising or publicity pertaining to
    distribution of the software without specific, written prior
    permission.

    SAM RUSHING DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
    INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
    NO EVENT SHALL SAM RUSHING BE LIABLE FOR ANY SPECIAL, INDIRECT OR
    CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
    OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
    NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

### Cookie management

The `http.cookies` module contains the following notice:

    Copyright 2000 by Timothy O'Malley <timo@alum.mit.edu>

                   All Rights Reserved

    Permission to use, copy, modify, and distribute this software
    and its documentation for any purpose and without fee is hereby
    granted, provided that the above copyright notice appear in all
    copies and that both that copyright notice and this permission
    notice appear in supporting documentation, and that the name of
    Timothy O'Malley  not be used in advertising or publicity
    pertaining to distribution of the software without specific, written
    prior permission.

    Timothy O'Malley DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
    SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
    AND FITNESS, IN NO EVENT SHALL Timothy O'Malley BE LIABLE FOR
    ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
    WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
    ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
    PERFORMANCE OF THIS SOFTWARE.

### Execution tracing

The `trace` module contains the following notice:

    portions copyright 2001, Autonomous Zones Industries, Inc., all rights...
    err...  reserved and offered to the public under the terms of the
    Python 2.2 license.
    Author: Zooko O'Whielacronx
    http://zooko.com/
    mailto:zooko@zooko.com

    Copyright 2000, Mojam Media, Inc., all rights reserved.
    Author: Skip Montanaro

    Copyright 1999, Bioreason, Inc., all rights reserved.
    Author: Andrew Dalke

    Copyright 1995-1997, Automatrix, Inc., all rights reserved.
    Author: Skip Montanaro

    Copyright 1991-1995, Stichting Mathematisch Centrum, all rights reserved.

    Permission to use, copy, modify, and distribute this Python software and
    its associated documentation for any purpose without fee is hereby
    granted, provided that the above copyright notice appears in all copies,
    and that both that copyright notice and this permission notice appear in
    supporting documentation, and that the name of neither Automatrix,
    Bioreason or Mojam Media be used in advertising or publicity pertaining to
    distribution of the software without specific, written prior permission.

### UUencode and UUdecode functions

The `uu` codec contains the following notice:

    Copyright 1994 by Lance Ellinghouse
    Cathedral City, California Republic, United States of America.
                           All Rights Reserved
    Permission to use, copy, modify, and distribute this software and its
    documentation for any purpose and without fee is hereby granted,
    provided that the above copyright notice appear in all copies and that
    both that copyright notice and this permission notice appear in
    supporting documentation, and that the name of Lance Ellinghouse
    not be used in advertising or publicity pertaining to distribution
    of the software without specific, written prior permission.
    LANCE ELLINGHOUSE DISCLAIMS ALL WARRANTIES WITH REGARD TO
    THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
    FITNESS, IN NO EVENT SHALL LANCE ELLINGHOUSE CENTRUM BE LIABLE
    FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
    OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

    Modified by Jack Jansen, CWI, July 1995:
    - Use binascii module to do the actual line-by-line conversion
      between ascii and binary. This results in a 1000-fold speedup. The C
      version is still 5 times faster, though.
    - Arguments more compliant with Python standard

### XML Remote Procedure Calls

The `xmlrpc.client` module contains the following notice:

        The XML-RPC client interface is

    Copyright (c) 1999-2002 by Secret Labs AB
    Copyright (c) 1999-2002 by Fredrik Lundh

    By obtaining, using, and/or copying this software and/or its
    associated documentation, you agree that you have read, understood,
    and will comply with the following terms and conditions:

    Permission to use, copy, modify, and distribute this software and
    its associated documentation for any purpose and without fee is
    hereby granted, provided that the above copyright notice appears in
    all copies, and that both that copyright notice and this permission
    notice appear in supporting documentation, and that the name of
    Secret Labs AB or the author not be used in advertising or publicity
    pertaining to distribution of the software without specific, written
    prior permission.

    SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
    TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-
    ABILITY AND FITNESS.  IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR
    BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
    DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
    WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
    ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
    OF THIS SOFTWARE.

### test_epoll

The `test.test_epoll` module contains the following notice:

    Copyright (c) 2001-2006 Twisted Matrix Laboratories.

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
    LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

### Select kqueue

The `select` module contains the following notice for the kqueue interface:

    Copyright (c) 2000 Doug White, 2006 James Knight, 2007 Christian Heimes
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.
    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

### SipHash24

The file `Python/pyhash.c` contains Marek Majkowski’ implementation of Dan Bernstein’s SipHash24 algorithm. It contains the following note:

    <MIT License>
    Copyright (c) 2013  Marek Majkowski <marek@popcount.org>

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
    </MIT License>

    Original location:
       https://github.com/majek/csiphash/

    Solution inspired by code from:
       Samuel Neves (supercop/crypto_auth/siphash24/little)
       djb (supercop/crypto_auth/siphash24/little2)
       Jean-Philippe Aumasson (https://131002.net/siphash/siphash24.c)

### strtod and dtoa

The file `Python/dtoa.c`, which supplies C functions dtoa and strtod for conversion of C doubles to and from strings, is derived from the file of the same name by David M. Gay, currently available from https://web.archive.org/web/20220517033456/http://www.netlib.org/fp/dtoa.c. The original file, as retrieved on March 16, 2009, contains the following copyright and licensing notice:

    /****************************************************************
     *
     * The author of this software is David M. Gay.
     *
     * Copyright (c) 1991, 2000, 2001 by Lucent Technologies.
     *
     * Permission to use, copy, modify, and distribute this software for any
     * purpose without fee is hereby granted, provided that this entire notice
     * is included in all copies of any software which is or includes a copy
     * or modification of this software and in all copies of the supporting
     * documentation for such software.
     *
     * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
     * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
     * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
     * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
     *
     ***************************************************************/

### OpenSSL

The modules `hashlib`, `posix` and `ssl` use the OpenSSL library for added performance if made available by the operating system. Additionally, the Windows and macOS installers for Python may include a copy of the OpenSSL libraries, so we include a copy of the OpenSSL license here. For the OpenSSL 3.0 release, and later releases derived from that, the Apache License v2 applies:

                                  Apache License
                            Version 2.0, January 2004
                         https://www.apache.org/licenses/

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### expat

The `pyexpat` extension is built using an included copy of the expat sources unless the build is configured `--with-system-expat`:

    Copyright (c) 1998, 1999, 2000 Thai Open Source Software Center Ltd
                                   and Clark Cooper

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

### libffi

The `_ctypes` C extension underlying the `ctypes` module is built using an included copy of the libffi sources unless the build is configured `--with-system-libffi`:

    Copyright (c) 1996-2008  Red Hat, Inc and others.

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
    DEALINGS IN THE SOFTWARE.

### zlib

The `zlib` extension is built using an included copy of the zlib sources if the zlib version found on the system is too old to be used for the build:

    Copyright (C) 1995-2011 Jean-loup Gailly and Mark Adler

    This software is provided 'as-is', without any express or implied
    warranty.  In no event will the authors be held liable for any damages
    arising from the use of this software.

    Permission is granted to anyone to use this software for any purpose,
    including commercial applications, and to alter it and redistribute it
    freely, subject to the following restrictions:

    1. The origin of this software must not be misrepresented; you must not
       claim that you wrote the original software. If you use this software
       in a product, an acknowledgment in the product documentation would be
       appreciated but is not required.

    2. Altered source versions must be plainly marked as such, and must not be
       misrepresented as being the original software.

    3. This notice may not be removed or altered from any source distribution.

    Jean-loup Gailly        Mark Adler
    jloup@gzip.org          madler@alumni.caltech.edu

### cfuhash

The implementation of the hash table used by the `tracemalloc` is based on the cfuhash project:

    Copyright (c) 2005 Don Owens
    All rights reserved.

    This code is released under the BSD license:

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

      * Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.

      * Redistributions in binary form must reproduce the above
        copyright notice, this list of conditions and the following
        disclaimer in the documentation and/or other materials provided
        with the distribution.

      * Neither the name of the author nor the names of its
        contributors may be used to endorse or promote products derived
        from this software without specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
    (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
    SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
    STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
    ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
    OF THE POSSIBILITY OF SUCH DAMAGE.

### libmpdec

The `_decimal` C extension underlying the `decimal` module is built using an included copy of the libmpdec library unless the build is configured `--with-system-libmpdec`:

    Copyright (c) 2008-2020 Stefan Krah. All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS "AS IS" AND
    ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
    ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
    FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
    DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
    OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
    HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
    OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

### W3C C14N test suite

The C14N 2.0 test suite in the `test` package (`Lib/test/xmltestdata/c14n-20/`) was retrieved from the W3C website at https://www.w3.org/TR/xml-c14n2-testcases/ and is distributed under the 3-clause BSD license:

    Copyright (c) 2013 W3C(R) (MIT, ERCIM, Keio, Beihang),
    All Rights Reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    * Redistributions of works must retain the original copyright notice,
      this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the original copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of the W3C nor the names of its contributors may be
      used to endorse or promote products derived from this work without
      specific prior written permission.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
    A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

### mimalloc

MIT License:

    Copyright (c) 2018-2021 Microsoft Corporation, Daan Leijen

    Permission is hereby granted, free of charge, to any person obtaining a copy
    of this software and associated documentation files (the "Software"), to deal
    in the Software without restriction, including without limitation the rights
    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the Software is
    furnished to do so, subject to the following conditions:

    The above copyright notice and this permission notice shall be included in all
    copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
    SOFTWARE.

### asyncio

Parts of the `asyncio` module are incorporated from uvloop 0.16, which is distributed under the MIT license:

    Copyright (c) 2015-2021 MagicStack Inc.  http://magic.io

    Permission is hereby granted, free of charge, to any person obtaining
    a copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
    LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
    OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
    WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

### Global Unbounded Sequences (GUS)

The file `Python/qsbr.c` is adapted from FreeBSD’s “Global Unbounded Sequences” safe memory reclamation scheme in subr_smr.c. The file is distributed under the 2-Clause BSD License:

    Copyright (c) 2019,2020 Jeffrey Roberson <jeff@FreeBSD.org>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:
    1. Redistributions of source code must retain the above copyright
       notice unmodified, this list of conditions, and the following
       disclaimer.
    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in the
       documentation and/or other materials provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE AUTHOR "AS IS" AND ANY EXPRESS OR
    IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
    IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
    NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
    THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.