Python计算字符宽度的方法
本文实例讲述了Python计算字符宽度的方法。分享给大家供大家参考，具体如下：
最近在用python写一个CLI小程序，其中涉及到计算字符宽度，目标是以友好的方式将一个长字符串截取为等宽的片段。
对于unicode字符，python的len函数可以准确的计算其中所包含的字符个数，但是个数并不代表宽度，如：
>>>len(u'你好a') 3
因此无法简单的使用这种方式来计算宽度。
GBK decode
首先我想到GBK编码，00–7F范围内的字符是一字节编码，其余是双字节编码，正好与字符的宽度大体一致，于是有了这样的投机取巧的办法（假设取8个宽度）：
>>> a = u'hello你好'
>>> b=a.encode('gbk')
>>> try:
... print b[:8].decode('gbk')
... except:
... print b[:7].decode('gbk')
...
hello你
如代码所示，首先将unicode的字符串进行GBK编码，然后截取8个字节的宽度后尝试用GBK解码，若解码失败，则少截取一个宽度，截取7个字节后使用GBK解码。
虽然初步解决了问题，但是这样做的硬伤很明显。首先代码不优雅，以试错的方式运行；其次GBK所能表示的字符有限，对于大量GBK编码以外的字符无法支持。
East_Asian_Width
徘徊很久之后，偶然发现 Unicode Character Database 标准中有East_Asian_Width 属性，并有以下可能值：
# East_Asian_Width (ea) ea ; A ; Ambiguous 不确定 ea ; F ; Fullwidth 全宽 ea ; H ; Halfwidth 半宽 ea ; N ; Neutral 中性 ea ; Na ; Narrow 窄 ea ; W ; Wide 宽
其中除A不确定外，F/H/N/Na/W都能很明确的知道宽度，如果保守起见，将A视为宽度为2的话，则很容易给出单个字符的宽度：
>>> import unicodedata
>>> def chr_width(c):
... if (unicodedata.east_asian_width(c) in ('F','W','A')):
... return 2
... else:
... return 1
>>> chr_width(u'你')
2
>>> chr_width(u'a')
1
到现在似乎已经可以满足要求了，但是实际使用中发现属性为A的字符真不少见，最典型的就是中文的双引号：
>>> chr_width(u'”') 2
在大多数等宽字体中，中文双引号都是只占一位宽的，如果一行里有多个中文双引号，则累加的误判宽度将会使截取效果大打折扣，无疑这也不是最好的办法。
urwid的解决方案
urwid 是一个成熟的python终端UI库，它在curses的基础之上包装了类似HTML的控件用以显示文本内容，如果有这方面的开发需求，非常推荐此库，比直接使用curses库方便很多，非常棒的是它对unicode的文本宽度截取非常准确，让我大为惊讶，于是翻开它的源码一探究竟，文本宽度计算方面其核心代码如下：
widths = [
(126, 1), (159, 0), (687, 1), (710, 0), (711, 1),
(727, 0), (733, 1), (879, 0), (1154, 1), (1161, 0),
(4347, 1), (4447, 2), (7467, 1), (7521, 0), (8369, 1),
(8426, 0), (9000, 1), (9002, 2), (11021, 1), (12350, 2),
(12351, 1), (12438, 2), (12442, 0), (19893, 2), (19967, 1),
(55203, 2), (63743, 1), (64106, 2), (65039, 1), (65059, 0),
(65131, 2), (65279, 1), (65376, 2), (65500, 1), (65510, 2),
(120831, 1), (262141, 2), (1114109, 1),
]
def get_width( o ):
"""Return the screen column width for unicode ordinal o."""
global widths
if o == 0xe or o == 0xf:
return 0
for num, wid in widths:
if o <= num:
return wid
return 1
如代码所示，首先根据unicode的官方EastAsianWidth 文档整理出字符宽度的范围表，然后使用unicode代码查表。使用之前的例子测试：
>>> get_width(ord(u'a')) 1 >>> get_width(ord(u'你')) 2 >>> get_width(ord(u'”')) 1
完全准确，而且在实际应用中的表现也比较好，是一个理想的解决方案，更多技巧请查阅urwid的old_str_util.py 源码。
更多关于Python相关内容感兴趣的读者可查看本站专题：《Python图片操作技巧总结》、《Python数据结构与算法教程》、《Python Socket编程技巧总结》、《Python函数使用技巧总结》、《Python字符串操作技巧汇总》、《Python入门与进阶经典教程》及《Python文件与目录操作技巧汇总》
希望本文所述对大家Python程序设计有所帮助。
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