docs: def expand_factor_conditions(s, env):
      """If env matches the expanded factor then return value else return ''.
  
      Example
      -------
      >>> s = 'py{33,34}: docformatter'
      >>> expand_factor_conditions(s, Env(name="py34", ...))
      "docformatter"
      >>> expand_factor_conditions(s, Env(name="py26", ...))
      ""
  
      """
      try:
          factor, value = re.split(r'\s*\:\s*', s)
      except ValueError:
          return s
  
      if matches_factor_conditions(factor, env):
          return value
      else:
          return ''