thomasballinger / wcwidth

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 certainly possible to use your Operating System's wcwidth() and wcswidth() 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.

Furthermore, testing (wcwidth-libc-comparator.py) has shown that libc wcwidth() is particularly out of date on most operating systems, reporting -1 for a great many characters that are actually a displayable width of 1 or 2.

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.

In python, 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.

However, if you were to print this to a Terminal Emulator, such as xterm, urxvt, Terminal.app, or PuTTY, it would consume 10 cells (columns) -- two for each symbol.

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.

Installation

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

pip install wcwidth

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

See the docstring for wcwidth(), general overview of return values:

• -1: indeterminate, such as combining characters.
• 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().

Developing

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

Generating 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)

Any subsequent changes were done by directly testing against the various libc implementations of POSIX-compliant Operating Systems, such as Mac OSX, Linux, and OpenSolaris.

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

It is my wish that combining characters are understood. Currently, any string containing combining characters will always return -1.

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 <[email protected]>

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.