re.sub with brackets, removing Japanese ruby characters

Given:

a = "[ruby(空,ruby=そら)]は[ruby(青,ruby=あお)]い。"
desired="空は青い。"

You can use alteration to remove the sub strings:

>>> s=re.sub(r'\[ruby\(|,ruby=[^)]+\)\]','',a)
>>> s
空は青い。
>>> s==desired
True

You can use

a = re.sub(r'\[ruby\(([^(),]*),[^()]*\)]', r'\1', a)

See the regex demo. Details:

• \[ruby\( - a [ruby( text
• ([^(),]*) - Group 1: any text other than (, ) and a comma, zero or more occurrences
• , - a comma
• [^()]* - zero or more chars other than ( and )
• \)] - a )] text.

See a Python demo:

import re
a = "[ruby(空,ruby=そら)]は[ruby(青,ruby=あお)]い。"
print( re.sub(r'\[ruby\(([^(),]*),[^()]*\)]', r'\1', a) )
# => 空は青い。