What is the difference between "Python interactive" and "Python 3" kernels
Interactive mode gives immediate feedback, i.e. every single line will be executed immediately, without possibility to script it i.e. following warnings: 


  &gt;&gt;&gt; if interactive:
  ...   print("do it")
  ... print("cant you?")
    File "&lt;stdin&gt;", line 3
      print("Done")
          ^
  SyntaxError: invalid syntax


so the fact that they are together confuses him, but if you seperate it


  &gt;&gt;&gt; if interactive:
  ...   print("do it")
  do it
  
  print("cant you?")
  cant you?


So the main point is to seperate, and be carefull with new command lines.

Python 3 is standard scripting python version.

Why differentiate? Interactive to test quick and dirty, Python3 to write scripts