When updating to macOS Catalina will the default Python installation get removed from my system?
From Xcode 11 Beta Release Notes:


  Scripting language runtimes such as Python, Ruby, and Perl are included in macOS for compatibility with legacy software. In future versions of macOS, scripting language runtimes won’t be available by default, and may require you to install an additional package. If your software depends on scripting languages, it’s recommended that you bundle the runtime within the app. (49764202)


So in Catalina these runtimes will still be available. 

Also, from the same document


  Use of Python 2.7 isn’t recommended. This version is included in macOS for compatibility with legacy software. Future versions of macOS won’t include Python 2.7. Instead, it’s recommended that you run python3 in Terminal. (51097165)