You are correct, and I apologize for not looking into this more deeply first.

For the specific case under discussion, ncoghlan added cache_info() on 30 Nov 2010 - https://github.com/python/cpython/commit/234515afe594e5f9ca1...

Previously, "Performance statistics stored in f.cache_hits and f.cache_misses." With the change "Significant statistics (maxsize, size, hits, misses) are available through the f.cache_info() named tuple."

There was no time when it was a tuple, much less in a tuple in a public release.

I'll look first at the namedtuples which have been present since at least 2.7.10.

The named tuples in "urllib/parse", "difflib", "inspect", "sched", and "doctest" were originally tuples. The decimal module's uses a DecimalTuple as a return value from to_tuple(), so I didn't check that history.

ssl uses a DefaultVerifyPaths added by tiran on 9 Jun 2013 - https://github.com/python/cpython/commit/6d7ad13a458afdf2cbd... . It did not replace a tuple. I assume _ASN1Object is the same way.

Now for the namedtuples in recent version control:

dis.py:_Instruction was added in https://github.com/python/cpython/commit/b39fd0c9b8dc6683924... . It did not replace a tuple.

aifc.py:_aifc_params replaces a tuple.

crypt.py:_Method replaced a class with a namedtuple in https://github.com/python/cpython/commit/daa5799cb8866785543... .

nntplib.py:GroupInfo and ArticleInfo added in https://github.com/python/cpython/commit/69ab95105f5105b8337... . It did not replace a tuple.

pkgutil.py:ModuleInfo replaces a tuple

platform.py:uname_result replaces a tuple

sndhdr.py:SndHeader replaces a tuple

sunau.py:_sunau_params replaces a tuple

tokenize.py:TokenInfo replaces a tuple

typing.py:nm_tpl ... is above my paygrade to understand. I believe it's required to be a namedtuple since that what it's trying to implement.

wave.py:_wave_params replaces a tuple.

Finally, urllib/robotparser.py appears to contain a bug in the following:

  req_rate = collections.namedtuple('req_rate',
                                    'requests seconds')
  entry.req_rate = req_rate
  entry.req_rate.requests = int(numbers[0])
  entry.req_rate.seconds = int(numbers[1])

As I read it, this should fail as the req_rate is immutable. This appears to be written by someone who thinks that it's a lightweight object. The commit is https://github.com/python/cpython/commit/960e848f0d32399824d... . It did not replace a tuple.

In conclusion, 8 of the current uses of namedtuple are not to emulate a tuple. 13 of the current uses replace a tuple.