Testing that a button operator has been executed

Hello developers !

I’d like to execute a function after a button operator has been executed.
Hereafter, once a file has been opened, the function read_now should be called.

class FileButton ( bpy.types.Operator ) :
    bl_idname = "one.button"
    bl_label = "My_File"

    def execute ( self, context ) :            
        bpy.ops.text.open ( 'INVOKE_DEFAULT' )        
        return { 'FINISHED' }

    # def read_now ( self ) :
           print ( "read something" )
     # return self.read_now() does not work, in case I had put read_now in this class
     # because return expects a string

def read_now () :
    print ( "read something" )

I thought I could put def read_now () in the class and return self.read_now in the ‘execute’ function but doesn’t work.
Other idea, putting def read_now () out and calling it on the return condition of the ‘execute’ function.
But how to do that ? Can ‘FINISHED’ be tested somehow ?

Thanks for any information !

Thanks for the help again !
As I understand there is no direct solution for doing it. I have to work on my python knowledge to understand the workaround with the decorator approach.