code: def parse_source(self, filename):
          
          callvisitor = FuncCallVisitor('sass_processor')
          tree = ast.parse(open(filename, 'rb').read())
          callvisitor.visit(tree)
          for sass_fileurl in callvisitor.sass_files:
              sass_filename = find_file(sass_fileurl)
              if not sass_filename or sass_filename in self.processed_files:
                  continue
              if self.delete_files:
                  self.delete_file(sass_filename, sass_fileurl)
              else:
                  self.compile_sass(sass_filename, sass_fileurl)
docs: Extract the statements from the given file, look for function calls
          `sass_processor(scss_file)` and compile the filename into CSS.