code: def merge(branch, fast_forward=False, commit=True, options=None):
      
      more_options = [
          fast_forward and '--ff' or '--no-ff',
          commit and '--commit' or '--no-commit',
      ] + (options and options or [])
      option_string = ' '.join(more_options)
      all_branches = branches()
      assert branch in all_branches, 'Missing branch: %s' % branch
      command = 'merge %s %s' % (option_string, branch)
      return run(command)
docs: Merge that branch into current branch
  
      fast_forward and commit add the eponymous options to the command