code: def format_string(target, kwargs):
    
    if not target:
      return target
    if callable(target):
      return target(**kwargs)
    if not isinstance(target, six.string_types):
      return target
    if '{' in target:
      return partial_format(target, **kwargs)
    if '%' in target:
      return target % kwargs
    return target
docs: Formats a string in any of three ways (or not at all).
  
    Args:
      target: The target string to format. This can be a function that takes a
          dict as its only argument, a string with {}- or %-based formatting, or
          a basic string with none of those. In the latter case, the string is
          returned as-is, but in all other cases the string is formatted (or the
          callback called) with the given kwargs.
          If this is None (or otherwise falsey), it is returned immediately.
      kwargs: The arguments to use for formatting.
          Passed to safe_format, %, or target if it's
          callable.