When playing with the Editline alternative to Readline, I noticed that “global” name completions can include duplicates:

>>> No
None                 NotADirectoryError(  NotImplementedError(
None                 NotImplemented      
>>> None
None None

It completed my line to “None”, but if you hit Tab again, it lists two duplicate options both identical to what I already have. The reason is that “None” is both a reserved keyword, and a member of the builtins module.

My patch avoids adding extra completions if a name has already been added. It also prioritizes the global namespace over builtins, so that say if you alias “int” to a non-callable, it is no longer listed with an opening bracket “(” suffix. Earlier behaviour:

>>> int = 81
>>> in
in     input( int    int(  

Now:

>>> in
in     input( int

Nice work.

An alternative approach is to make "matches" a dict. And instead of

    if match not in seen:
        seen.add(word)
        matches.append(match)

use just

    matches[word] = match

I don't know what approach is better.

Added other minor comments on Rietveld.

New changeset 4799615f4f26 by Martin Panter in branch '3.4':
Issue #25663: Make rlcompleter avoid duplicate global names
https://hg.python.org/cpython/rev/4799615f4f26

New changeset 4ed70c568baf by Martin Panter in branch '3.5':
Issue #25663: Merge rlcompleter fix from 3.4 into 3.5
https://hg.python.org/cpython/rev/4ed70c568baf

New changeset 96fb9daf64a5 by Martin Panter in branch 'default':
Issue #25663: Merge rlcompleter fix from 3.5
https://hg.python.org/cpython/rev/96fb9daf64a5

New changeset f742c31491e3 by Martin Panter in branch 'default':
Issue #25663: Update rlcompleter test for new 3.6 behaviour
https://hg.python.org/cpython/rev/f742c31491e3

New changeset d3a9b055206c by Martin Panter in branch '2.7':
Issue #25663: Make rlcompleter avoid duplicate global names
https://hg.python.org/cpython/rev/d3a9b055206c

I chose to keep my strategy of using the set. Using a dictionary to hold the matches could mess up the order, although it looks like Readline sorts the matches before displaying them.