code: def find_source_lines(self):
          
          strs = trace.find_strings(self.filename)
          lines = trace.find_lines_from_code(self.fn.__code__, strs)
          self.firstcodelineno = sys.maxint
          for lineno in lines:
              self.firstcodelineno = min(self.firstcodelineno, lineno)
              self.sourcelines.setdefault(lineno, 0)
          if self.firstcodelineno == sys.maxint:
              self.firstcodelineno = self.firstlineno
docs: Mark all executable source lines in fn as executed 0 times.