[IPython-user] Re: OSX tab completion

Fernando Perez Fernando.Perez at colorado.edu
Fri Apr 1 20:03:27 CST 2005

Robert Kern wrote:

>>Robert, does this mean you also have the same problem?  I didn't realize 
>>that this was a widespread OSX issue.  If someone has a definitive 
>>solution/answer to this, please let me know so I can add this 
>>information to the user's guide for future reference.
> Yes, I have the same problem. I am using my own build of readline 5.0. 
> Unless I get more info very soon, this is also the build that will be in 
> MacEnthon.

OK, this is definitely controlled by the python build of readline.c.  Here are 
some pointers.  From the Gnu readline manual at


I found this note:

Variable: int rl_completion_append_character
     When a single completion alternative matches at the end of the command 
line, this character is appended to the inserted completion text. The default 
is a space character (` '). Setting this to the null character (`\0') prevents 
anything being appended automatically. This can be changed in 
application-specific completion functions to provide the "most sensible word 
separator character" according to an application-specific command line syntax 

Indeed, in the Python 2.4.1 source tree, in Modules/readline.c, around line 
717 we find:

         rl_completion_append_character ='\0';

Now, a grep of the whole source tree reveals:

planck[Python-2.4.1]> egrep -rn HAVE_RL_COMPLETION_APPEND_CHARACTER *
Modules/readline.c:487:#ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER
Modules/readline.c:579:#ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER
Modules/readline.c:716:#ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER
Modules/readline.c:858:#ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER

So what appears to occur is that under OSX, for whatever reason, configure is 
NOT defining the HAVE_RL_COMPLETION_APPEND_CHARACTER macro, and hence the 
rl_completion_append_character is never reset to '\0'.  In this case, as 
indicated above, the readline library will default to appending a space.

With this info, it should be possible to track down why under OSX (at least 
under certain builds), the HAVE_RL_COMPLETION_APPEND_CHARACTER macro is not 
being defined.  Worse case, you could just modify readline.c to make the above 
change unconditionally, without worrying about this macro (just strip the 

Note that this variable is NOT exposed publically by the python readline API, 
so this has to be fixed at build time, you can't reset it later at runtime via 
any kind of user setting (at least not that I can see).

I hope this helps some.



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