Support set operations in regular expression character classes

Feature or enhancement

Implement the set operations of Unicode Technical Standard #18 RL1.3 in re character classes, together with nested sets.

gh-74534 added FutureWarnings in Python 3.7 for the ambiguous constructs (--, &&, ~~, ||, and a leading [) as preparation for this syntax; this issue turns them into operators.

Two character sets are combined by an operator, where an operand may be a nested set in brackets:

• [A--B] — difference: a character in A but not in B.
• [A&&B] — intersection: a character in both A and B.
• [A||B] — union: a character in A or B.
• [A~~B] — symmetric difference: a character in A or B but not both.

Operators have no precedence and apply left to right; nested sets are used to group. A leading ^ complements the whole result.

For example, [a-z--[aeiou]] matches an ASCII lowercase consonant and [\w&&[a-z]] matches an ASCII lowercase letter.

Linked PRs

• gh-152153
• gh-152154
• gh-152214
• gh-153022

Bắt đầu bằng cách đọc cách re của Python xử lý lớp ký tự và Unicode Technical Standard #18 RL1.3. Xác nhận việc hoàn thành dựa trên các ví dụ được liệt kê về hiệu, giao, hợp, hiệu đối xứng, lồng nhau, xử lý từ trái sang phải và phần bù.