[eesmith]

As a concrete example, in Python 1.5.2, urlparse.py:urlparse returned a 6-element tuple:

  # Parse a URL into 6 components:
  # <scheme>://<netloc>/<path>;<params>?<query>#<fragment>
  # Return a 6-tuple: (scheme, netloc, path, params, query, fragment).
  # Note that we don't break the components up in smaller bits
  # (e.g. netloc is a single string) and we don't expand % escapes.
  def urlparse(url, scheme = '', allow_fragments = 1):
      ...
      tuple = scheme, netloc, url, params, query, fragment
      _parse_cache[key] = tuple
      return tuple

This API was around for years, with people using tuple indexing either explicitly or through destructuring assignment.

This was replaced with a namedtuple. The following is from Python 2.7.10:

  class ParseResult(namedtuple('ParseResult', 'scheme netloc path params query fragment'), ResultMixin):

    __slots__ = ()

    def geturl(self):
        return urlunparse(self)


  def urlparse(url, scheme='', allow_fragments=True):
    """Parse a URL into 6 components:
    <scheme>://<netloc>/<path>;<params>?<query>#<fragment>
    Return a 6-tuple: (scheme, netloc, path, params, query, fragment).
    Note that we don't break the components up in smaller bits
    (e.g. netloc is a single string) and we don't expand % escapes."""
    tuple = urlsplit(url, scheme, allow_fragments)
    scheme, netloc, url, query, fragment = tuple
    if scheme in uses_params and ';' in url:
        url, params = _splitparams(url)
    else:
        params = ''
    return ParseResult(scheme, netloc, url, params, query, fragment)

The old tuple-based API still works, so it doesn't break backwards compatibility, while it also gives people the ability to migrate to an attribute-based API.

That said, it's very hard to remove the old API. The latest version of Python, in url/parse.py:urlparse, still supports tuple-based indexing.

Perhaps Python 4 will remove that behavior? Probably not. At the very least there would need to be a namedtuplemigration type which gives a warning if the old tuple API is used when only attribute lookup is expected.

[masklinn]

> This API was around for years, with people using tuple indexing either explicitly or through destructuring assignment.

FWIW destructuring assignment uses the iteration protocol[0] not indexing.

[0] which can fallback on indexing if there is no explicit iteration support, IME that tends to be more unhelpful than convenient

[eesmith]

Hmm, I think meant to say something like "using either explicit tuple indexing or through destructuring assignment". Words, mixed up, they were. But yes, what I wrote was wrong.