wcwidth 0.1.6

Measures number of Terminal column cells of wide-character codes

Introduction

This Library is mainly for those implementing a Terminal Emulator, or programs that carefully produce output to be interpreted by one.

Problem Statement: When printed to the screen, the length of the string is usually equal to the number of cells it occupies. However, there are categories of characters that occupy 2 cells (full-wide), and others that occupy 0.

Solution: POSIX.1-2001 and POSIX.1-2008 conforming systems provide wcwidth(3) and wcswidth(3) C functions of which this python module’s functions precisely copy. These functions return the number of cells a unicode string is expected to occupy.

This library aims to be forward-looking, portable, and most correct. The most current release of this API is based on the Unicode Standard release files:

EastAsianWidth-8.0.0.txt

2015-02-10, 21:00:00 GMT [KW, LI]

DerivedGeneralCategory-8.0.0.txt

2015-02-13, 13:47:11 GMT [MD]

Installation

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

pip install wcwidth

Example

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'
>>> text_len = wcswidth(text)
>>> print(u' ' * (80 - text_len) + text)

wcwidth, wcswidth

Use function wcwidth() to determine the length of a single unicode character, and wcswidth() to determine the length of a several, or a string of unicode characters.

Briefly, return values of function wcwidth() are:

-1

Indeterminate (not printable).

0

Does not advance the cursor, such as NULL or Combining.

2

Characters of category East Asian Wide (W) or East Asian Full-width (F) which are displayed using two terminal cells.

1

All others.

Function wcswidth() simply returns the sum of all values for each character along a string, or -1 when it occurs anywhere along a string.

More documentation is available using pydoc:

$ pydoc wcwidth

Caveats

This library attempts to determine the printable width by an unknown targeted terminal emulator. It does not provide any ability to discern what the target emulator software, version, of level of support is. Results may vary!

A crude method of determining the level of unicode support by the target emulator may be performed using the VT100 Query Cursor Position sequence.

The libc version of wcwidth(3) is often several unicode releases behind, and therefor several levels of support lower than this python library. You may determine an exacting list of these discrepancies using the project file wcwidth-libc-comparator.py.

Developing

Install wcwidth in editable mode:

pip install -e.

Install developer requirements:

pip install -r requirements-develop.txt

Execute unit tests using tox:

tox

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/DerivedGeneralCategory.txt

And generates the table files:

• wcwidth/table_wide.py

• wcwidth/table_zero.py

Uses

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 are found in the bin/ folder of this project’s source code. They are not distributed.

History

0.1.6 2016-01-08 Production/Stable

• LICENSE file now included with distribution.

0.1.5 2015-09-13 Alpha

• Bugfix: Resolution of “combining character width” issue, most especially those that previously returned -1 now often (correctly) return 0. resolved by Philip Craig via PR #11.

• Deprecated: The module path wcwidth.table_comb is no longer available, it has been superseded by module path wcwidth.table_zero.

0.1.4 2014-11-20 Pre-Alpha

• 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).

• Feature: added static analysis (prospector) to testing framework.

0.1.3 2014-10-29 Pre-Alpha

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

0.1.2 2014-10-28 Pre-Alpha

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

0.1.1 2014-05-14 Pre-Alpha

• Initial release to pypi, Based on Unicode Specification 6.3.0

This code was originally derived directly from C code of the same name, whose latest version is available at http://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c:

* Markus Kuhn -- 2007-05-26 (Unicode 5.0)
*
* 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.