unidecode/README.rst

Unidecode, lossy ASCII transliterations of Unicode text
=======================================================

It often happens that you have text data in Unicode, but you need to
represent it in ASCII. For example when integrating with legacy code that
doesn't support Unicode, or for ease of entry of non-Roman names on a US
keyboard, or when constructing ASCII machine identifiers from human-readable
Unicode strings that should still be somewhat intelligible. A popular example
of this is when making an URL slug from an article title.

**Unidecode is not a replacement for fully supporting Unicode for strings in
your program. There are a number of caveats that come with its use,
especially when its output is directly visible to users. Please read the rest
of this README before using Unidecode in your project.**

In most of examples listed above you could represent Unicode characters as
``???`` or ``\\15BA\\15A0\\1610``, to mention two extreme cases. But that's
nearly useless to someone who actually wants to read what the text says.

What Unidecode provides is a middle road: the function ``unidecode()`` takes
Unicode data and tries to represent it in ASCII characters (i.e., the
universally displayable characters between 0x00 and 0x7F), where the
compromises taken when mapping between two character sets are chosen to be
near what a human with a US keyboard would choose.

The quality of resulting ASCII representation varies. For languages of
western origin it should be between perfect and good. On the other hand
transliteration (i.e., conveying, in Roman letters, the pronunciation
expressed by the text in some other writing system) of languages like
Chinese, Japanese or Korean is a very complex issue and this library does
not even attempt to address it. It draws the line at context-free
character-by-character mapping. So a good rule of thumb is that the further
the script you are transliterating is from Latin alphabet, the worse the
transliteration will be.

Generally Unidecode produces better results than simply stripping accents from
characters (which can be done in Python with built-in functions). It is based
on hand-tuned character mappings that for example also contain ASCII
approximations for symbols and non-Latin alphabets.

**Note that some people might find certain transliterations offending.** Most
common examples include characters that are used in multiple languages. A user
expects a character to be transliterated in their language but Unidecode uses a
transliteration for a different language. It's best to not use Unidecode for
strings that are directly visible to users of your application. See also the
*Frequently Asked Questions* section for more info on common problems.

This is a Python port of ``Text::Unidecode`` Perl module by Sean M. Burke
<sburke@cpan.org>.


Module content
--------------

This library contains a function that takes a string object, possibly
containing non-ASCII characters, and returns a string that can be safely
encoded to ASCII::

    >>> from unidecode import unidecode
    >>> unidecode('kožušček')
    'kozuscek'
    >>> unidecode('30 \U0001d5c4\U0001d5c6/\U0001d5c1')
    '30 km/h'
    >>> unidecode('\u5317\u4EB0')
    'Bei Jing '

You can also specify an *errors* argument to ``unidecode()`` that determines
what Unidecode does with characters that are not present in its transliteration
tables. The default is ``'ignore'`` meaning that Unidecode will ignore those
characters (replace them with an empty string). ``'strict'`` will raise a
``UnidecodeError``. The exception object will contain an *index* attribute that
can be used to find the offending character. ``'replace'`` will replace them
with ``'?'`` (or another string, specified in the *replace_str* argument).
``'preserve'`` will keep the original, non-ASCII character in the string. Note
that if ``'preserve'`` is used the string returned by ``unidecode()`` will not
be ASCII-encodable!::

    >>> unidecode('\ue000') # unidecode does not have replacements for Private Use Area characters
    ''
    >>> unidecode('\ue000', errors='strict')
    Traceback (most recent call last):
    ...
    unidecode.UnidecodeError: no replacement found for character '\ue000' in position 0

A utility is also included that allows you to transliterate text from the
command line in several ways. Reading from standard input::

    $ echo hello | unidecode
    hello

from a command line argument::

    $ unidecode -c hello
    hello

or from a file::

    $ unidecode hello.txt
    hello

The default encoding used by the utility depends on your system locale. You can
specify another encoding with the ``-e`` argument. See ``unidecode --help`` for
a full list of available options.

Requirements
------------

Nothing except Python itself. Unidecode supports Python 3.5 or later.

You need a Python build with "wide" Unicode characters (also called "UCS-4
build") in order for Unidecode to work correctly with characters outside of
Basic Multilingual Plane (BMP). Common characters outside BMP are bold, italic,
script, etc. variants of the Latin alphabet intended for mathematical notation.
Surrogate pair encoding of "narrow" builds is not supported in Unidecode.

If your Python build supports "wide" Unicode the following expression will
return True::

    >>> import sys
    >>> sys.maxunicode > 0xffff
    True

See `PEP 261 <https://www.python.org/dev/peps/pep-0261/>`_ for details
regarding support for "wide" Unicode characters in Python.


Installation
------------

To install the latest version of Unidecode from the Python package index, use
these commands::

    $ pip install unidecode

To install Unidecode from the source distribution and run unit tests, use::

    $ python setup.py install
    $ python setup.py test

Frequently asked questions
--------------------------

German umlauts are transliterated incorrectly
    Latin letters "a", "o" and "u" with diaeresis are transliterated by
    Unidecode as "a", "o", "u", *not* according to German rules "ae", "oe",
    "ue". This is intentional and will not be changed. Rationale is that these
    letters are used in languages other than German (for example, Finnish and
    Turkish). German text transliterated without the extra "e" is much more
    readable than other languages transliterated using German rules. A
    workaround is to do your own replacements of these characters before
    passing the string to ``unidecode()``.

Japanese Kanji is transliterated as Chinese
    Same as with Latin letters with accents discussed in the answer above, the
    Unicode standard encodes letters, not letters in a certain language or
    their meaning. With Japanese and Chinese this is even more evident because
    the same letter can have very different transliterations depending on the
    language it is used in. Since Unidecode does not do language-specific
    transliteration (see next question), it must decide on one. For certain
    characters that are used in both Japanese and Chinese the decision was to
    use Chinese transliterations. If you intend to transliterate Japanese,
    Chinese or Korean text please consider using other libraries which do
    language-specific transliteration, such as `Unihandecode
    <https://github.com/miurahr/unihandecode>`_.

Unidecode should support localization (e.g. a language or country parameter, inspecting system locale, etc.)
    Language-specific transliteration is a complicated problem and beyond the
    scope of this library. Changes related to this will not be accepted. Please
    consider using other libraries which do provide this capability, such as
    `Unihandecode <https://github.com/miurahr/unihandecode>`_.

Unidecode should automatically detect the language of the text being transliterated
    Language detection is a completely separate problem and beyond the scope of
    this library.

Unidecode should use a permissive license such as MIT or the BSD license.
    The maintainer of Unidecode believes that providing access to source code
    on redistribution is a fair and reasonable request when basing products on
    voluntary work of many contributors. If the license is not suitable for
    you, please consider using other libraries, such as `text-unidecode
    <https://github.com/kmike/text-unidecode>`_.

Unidecode produces completely wrong results (e.g. "u" with diaeresis transliterating as "A 1/4 ")
    The strings you are passing to Unidecode have been wrongly decoded
    somewhere in your program. For example, you might be decoding utf-8 encoded
    strings as latin1. With a misconfigured terminal, locale and/or a text
    editor this might not be immediately apparent. Inspect your strings with
    ``repr()`` and consult the
    `Unicode HOWTO <https://docs.python.org/3/howto/unicode.html>`_.

Why does Unidecode not replace \\u and \\U backslash escapes in my strings?
    Unidecode knows nothing about escape sequences. Interpreting these sequences
    and replacing them with actual Unicode characters in string literals is the
    task of the Python interpreter. If you are asking this question you are
    very likely misunderstanding the purpose of this library. Consult the
    `Unicode HOWTO <https://docs.python.org/3/howto/unicode.html>`_ and possibly
    the ``unicode_escape`` encoding in the standard library.

I've upgraded Unidecode and now some URLs on my website return 404 Not Found.
    This is an issue with the software that is running your website, not
    Unidecode. Occasionally, new versions of Unidecode library are released
    which contain improvements to the transliteration tables. This means that
    you cannot rely that ``unidecode()`` output will not change across
    different versions of Unidecode library. If you use ``unidecode()`` to
    generate URLs for your website, either generate the URL slug once and store
    it in the database or lock your dependency of Unidecode to one specific
    version.

Some of the issues in this section are discussed in more detail in `this blog
post <https://www.tablix.org/~avian/blog/archives/2013/09/python_unidecode_release_0_04_14/>`_.


Performance notes
-----------------

By default, ``unidecode()`` optimizes for the use case where most of the strings
passed to it are already ASCII-only and no transliteration is necessary (this
default might change in future versions).

For performance critical applications, two additional functions are exposed:

``unidecode_expect_ascii()`` is optimized for ASCII-only inputs (approximately
5 times faster than ``unidecode_expect_nonascii()`` on 10 character strings,
more on longer strings), but slightly slower for non-ASCII inputs.

``unidecode_expect_nonascii()`` takes approximately the same amount of time on
ASCII and non-ASCII inputs, but is slightly faster for non-ASCII inputs than
``unidecode_expect_ascii()``.

Apart from differences in run time, both functions produce identical results.
For most users of Unidecode, the difference in performance should be
negligible.


Source
------

You can get the latest development version of Unidecode with::

    $ git clone https://www.tablix.org/~avian/git/unidecode.git

There is also an official mirror of this repository on GitHub at
https://github.com/avian2/unidecode


Contact
-------

Please make sure to read the `Frequently asked questions`_ section above before
contacting the maintainer.

Bug reports, patches and suggestions for Unidecode can be sent to
tomaz.solc@tablix.org.

Alternatively, you can also open a ticket or pull request at
https://github.com/avian2/unidecode


Copyright
---------

Original character transliteration tables:

Copyright 2001, Sean M. Burke <sburke@cpan.org>, all rights reserved.

Python code and later additions:

Copyright 2022, Tomaž Šolc <tomaz.solc@tablix.org>

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option)
any later version.

This program is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc., 51
Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.  The programs and
documentation in this dist are distributed in the hope that they will be
useful, but without any warranty; without even the implied warranty of
merchantability or fitness for a particular purpose.

..
    vim: set filetype=rst: