Python 正则表达式模块中的简单案例折叠与完整案例折叠

Question

这是我要问的模块：https://pypi.org/project/regex/，它是 Matthew Barnett 的 regex。

在项目描述页面中，V0 和 V1 之间的行为差异表述为（注意粗体部分）：

Old vs new behaviour

In order to be compatible with the re module, this module has 2 behaviours:

Version 0 behaviour (old behaviour, compatible with the re module):

Please note that the re module’s behaviour may change over time, and I’ll endeavour to match that behaviour in version 0.

Indicated by the VERSION0 or V0 flag, or (?V0) in the pattern.

Case-insensitive matches in Unicode use simple case-folding by default.

Version 1 behaviour (new behaviour, possibly different from the re module):

Indicated by the VERSION1 or V1 flag, or (?V1) in the pattern.

Case-insensitive matches in Unicode use full case-folding by default.

If no version is specified, the regex module will default to regex.DEFAULT_VERSION.

我自己试了几个例子，但没弄清楚它的作用：

Python 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import regex
>>> r = regex.compile("(?V0i)и")
>>> r
regex.Regex('(?V0i)и', flags=regex.I | regex.V0)
>>> r.search("И")
<regex.Match object; span=(0, 1), match='И'>
>>> regex.search("(?V0i)é", "É")
<regex.Match object; span=(0, 1), match='É'>
>>> regex.search("(?V0i)é", "E")
>>> regex.search("(?V1i)é", "E")

简单折叠和完整折叠有什么区别？或者您能否提供一个示例，其中（不区分大小写的）正则表达式匹配 V1 中的某些内容但不匹配 V0 中的内容？

Answer 1

它在 Unicode case folding table 之后。摘录：

# The entries in this file are in the following machine-readable format:
#
# <code>; <status>; <mapping>; # <name>
#
# The status field is:
# C: common case folding, common mappings shared by both simple and full mappings.
# F: full case folding, mappings that cause strings to grow in length. Multiple characters are separated by spaces.
# S: simple case folding, mappings to single characters where different from F.

[...]

# Usage:
#  A. To do a simple case folding, use the mappings with status C + S.
#  B. To do a full case folding, use the mappings with status C + F.

只有少数特殊字符的折叠方式不同，例子很小，大写的拉丁升号：

00DF; F; 0073 0073; # LATIN SMALL LETTER SHARP S

[...]

1E9E; F; 0073 0073; # LATIN CAPITAL LETTER SHARP S
1E9E; S; 00DF; # LATIN CAPITAL LETTER SHARP S

Python 正则表达式模块中的简单案例折叠与完整案例折叠

Simple case folding vs full case folding in Python regex module

python

regex

python-regex