code: def make_unique_name(base, existing=[], format="%s_%s"):
      
      count = 2
      name = base
      while name in existing:
          name = format % (base, count)
          count += 1
  
      return name
docs: Return a name, unique within a context, based on the specified name.
  
      @param base: the desired base name of the generated unique name.
      @param existing: a sequence of the existing names to avoid returning.
      @param format: a formatting specification for how the name is made unique.