Python/RegEx/String with combination of a and bs

Contents:

• 📁 String has a followed by 0 or 1 bs
• 📁 String has a followed by 0 or more bs
• 📁 String has a followed by 1 or more bs
• 📁 String has a followed by 2-3 bs
• 📁 String has a followed by 3 bs