code: def get_csig(self):
          
          try:
              return self.ninfo.csig
          except AttributeError:
              pass
  
          contents = self.get_contents()
          csig = SCons.Util.MD5signature(contents)
          self.get_ninfo().csig = csig
          return csig
docs: Generate a node's content signature, the digested signature
          of its content.
  
          node - the node
          cache - alternate node to use for the signature cache
          returns - the content signature