Please see http://bugs.python.org/issue5845, especially the last two comments: http://bugs.python.org/issue5845#msg215784, which requested that a new bug report be opened for this issue.

To summarize, the previous bug was to enable tab completion in the interpreter. There was discussion and it was figured out that it could be arranged that tab indentation and completion could work at the same time. (If you are at the start of a line, possibly a "... " prompt line, tab should indent. If you are to the right of any non-whitespace character, then you should tab complete).

From the other bug:

"This issue [tab indent] should have gone back to being a release blocker after the alpha release to fix the tab-as-indent issue, but obviously that didn't happen (I forgot about it myself).  Please open a new issue requesting a fix for this bug (that tab doesn't work as indent at the ... prompt), referencing the discussion in this issue."