We need to check whether __builtins__ is a dict versus a module so as to
assign the appropriate input function to scanf. In an imported module,
__builtins__ is a dict, whereas in the main application which is executed,
it is a module. The conditionals basically say that if we were imported, check
if raw_input was in the dictionary, otherwise check if it is defined in the
main module, via hasattr, or else assign input to scanf, which is to say
the script is using Python3. All of this is done to have a well-defined,
universal scanf for taking user inputs, which runs in both Python2 and
Python3.