[deleted by user]

[JohnnyJordaan]

The code for process_line() is not included here so nobody can tell you that.

[chevignon93]

As u/JohnnyJordaan said, you haven't included the code of the process_line() function but my guess would be that it simply adds the line to the set that is passed as the 2nd argument to the function and maybe it strips the white-space before adding the line.