code: def get_content_hash(self):
          
          if not self.rexists():
              return SCons.Util.MD5signature('')
          fname = self.rfile().get_abspath()
          try:
              cs = SCons.Util.MD5filesignature(fname,
                  chunksize=SCons.Node.FS.File.md5_chunksize*1024)
          except EnvironmentError as e:
              if not e.filename:
                  e.filename = fname
              raise
          return cs
docs: Compute and return the MD5 hash for this file.