>>556
>>560にはバグ有り
>>> import re
>>> text = 'hoge abc amnc axyzc fuga abstract auuc aaac'
>>> re.sub(r'\ba(\w+)c\b', lambda s: s.group(0).replace(s.group(1), s.group(1).upper()), text)
'hoge aBc aMNc aXYZc fuga abstract aUUc AAac'　←最後のaaacがaAAcとならない
>>>
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
バグ修正版
>>> re.sub(r'\b(a)(\w+)(c)\b', lambda m: m.group(1)+m.group(2).upper()+m.group(3), text)
'hoge aBc aMNc aXYZc fuga abstract aUUc aAAc'
>>>