wcwidth 0.1.4

Measures number of Terminal column cells of wide-character codes

Introduction

This API is mainly for Terminal Emulator implementors – any python program that attempts to determine the printable width of a string on a Terminal. It is implemented in python (no C library calls) and has no 3rd-party dependencies.

It is certainly possible to use your Operating System’s wcwidth(3) and wcswidth(3) calls if it is POSIX-conforming, but this would not be possible on non-POSIX platforms, such as Windows, or for alternative Python implementations, such as jython. It is also commonly many releases older than the most current Unicode Standard release files, which this project aims to track.

The most current release of this API is based from Unicode Standard release 7.0.0, dated 2014-02-28, 23:15:00 GMT [KW, LI] for table generated by file EastAsianWidth-7.0.0.txt and 2014-02-07, 18:42:08 GMT [MD] for DerivedCombiningClass-7.0.0.txt.

Installation

The stable version of this package is maintained on pypi, install using pip:

pip install wcwidth

Problem

You may have noticed some characters especially Chinese, Japanese, and Korean (collectively known as the CJK Unified Ideographs) consume more than 1 terminal cell. If you ask for the length of the string, u'コンニチハ' (Japanese: Hello), it is correctly determined to be a length of 5 using the len() built-in.

However, if you were to print this to a Terminal Emulator, such as xterm, urxvt, Terminal.app, PuTTY, or iTerm2, it would consume 10 cells (columns). This causes problems for many of the text-alignment functions, such as rjust(). On an 80-wide terminal, the following would wrap along the margin, instead of displaying it right-aligned as desired:

>>> text = u'コンニチハ'
>>> print(text.rjust(80))
                                                                             コン
ニチハ

Solution

This API allows one to determine the printable length of these strings, that the length of wcwidth(u'コ') is reported as 2, and wcswidth(u'コンニチハ') as 10.

This allows one to determine the printable effects of displaying CJK characters on a terminal emulator.

wcwidth, wcswidth

Use wcwidth to determine the length of a single character, and wcswidth to determine the length of a string of characters.

To Display u'コンニチハ' right-adjusted on screen of 80 columns:

>>> from wcwidth import wcswidth
>>> text = u'コンニチハ'
>>> print(u' ' * (80 - wcswidth(text)) + text)
                                                                       コンニチハ

Values

A general overview of return values:

• -1: indeterminate (see Todo).

• 0: do not advance the cursor, such as NULL.

• 2: East_Asian_Width property values W and F (Wide and Full-width).

• 1: all others.

wcswidth() simply returns the sum of all values along a string, or -1 if it has occurred for any value returned by wcwidth(). A more exacting list of conditions and return values may be found in the docstring for wcwidth().

Discrepacies

There may be discrepancies with the determined printable width of of characters by wcwidth and the results of any given terminal emulator – most commonly, emulators are using your Operating System’s wcwidth(3) implementation which is often based on tables much older than the most current Unicode Specification. Python’s determination of non-zero combining characters may also be based on an older specification.

You may determine an exacting list of these discrepancies using files wcwidth-libc-comparator.py and wcwidth-combining-comparator.py

Developing

Execute the command python setup.py develop to prepare an environment for running tests (python setup.py test), updating tables ( python setup.py update) or using any of the scripts in the bin/ sub-folder. These files are only made available in the source repository.

Updating Tables

The command python setup.py update will fetch the following resources:

• http://www.unicode.org/Public/UNIDATA/EastAsianWidth.txt

• http://www.unicode.org/Public/UNIDATA/extracted/DerivedCombiningClass.txt

And generate the table files wcwidth/table_wide.py and wcwidth/table_comb.py.

wcwidth.c

This code was originally derived directly from C code of the same name, whose latest version is available at: wcwidth.c And is authored by Markus Kuhn – 2007-05-26 (Unicode 5.0)

Examples

This library is used in:

• jquast/blessed, a simplified wrapper around curses.

• jonathanslenders/python-prompt-toolkit, a Library for building powerful interactive command lines in Python.

Additional tools for displaying and testing wcwidth is found in the bin/ folder of this project (github link: wcwidth/bin). They are not distributed as a script or part of the module.

Todo

Though some of the most common (“zero-width”) combining characters are understood by wcswidth, there are still many edge cases that need to be covered, especially certain kinds of sequences such as those containing Control-Sequence-Inducer (CSI).

License

The original license is as follows:

Permission to use, copy, modify, and distribute this software
for any purpose and without fee is hereby granted. The author
disclaims all warranties with regard to this software.

No specific licensing is specified, and Mr. Kuhn resides in the UK which allows some protection from Copyrighting. As this derivative is based on US Soil, an OSI-approved license that appears most-alike has been chosen, the MIT license:

The MIT License (MIT)

Copyright (c) 2014 <[e-mail]>

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.

Changes

0.1.4

• Feature: wcswidth() now determines printable length for (most) combining characters. The developer’s tool bin/wcwidth-browser.py is improved to display combining characters when provided the --combining option (Thomas Ballinger and Leta Montopoli PR #5).

• added static analysis (prospector) to testing framework.

0.1.3

• Bugfix: 2nd parameter of wcswidth was not honored. (Thomas Ballinger, PR #4).

0.1.2

• Updated tables to Unicode Specification 7.0.0. (Thomas Ballinger, PR #3).

0.1.1

• Initial release to pypi, Based on Unicode Specification 6.3.0