code: def _pip_list(self, stdout, stderr, prefix=None):
          
          result = stdout  # A dict
          linked = self.linked(prefix)
  
          pip_only = []
  
          linked_names = [self.split_canonical_name(l)[0] for l in linked]
  
          for pkg in result:
              name = self.split_canonical_name(pkg)[0]
              if name not in linked_names:
                  pip_only.append(pkg)
              # FIXME: NEED A MORE ROBUST WAY!
  #            if '<pip>' in line and '#' not in line:
  #                temp = line.split()[:-1] + ['pip']
  #                temp = '-'.join(temp)
  #                if '-(' in temp:
  #                    start = temp.find('-(')
  #                    end = temp.find(')')
  #                    substring = temp[start:end+1]
  #                    temp = temp.replace(substring, '')
  #                result.append(temp)
  
          return pip_only
docs: Callback for `pip_list`.