Review time!
+ elif "[" in text:
+ self.matches = self.dict_key_matches(text)
Does this complete only dicts? What about other mappings? What about other sequences implementing __getitem__? One of the function name and the function docstring (“Compute matches when text contains a [”) is wrong.
I’m not familiar with rlcompleter’s internals, so I’d like a few comments sprinkled in the code.
Please wrap your lines at 79 columns, and follow other advice given at http://www.python.org/dev/patches/ for the next version of your patch.
+ The evaluation of the part before the '[' could be enhanced.
This belongs in a comment or a test, not the docstring.
+ 'DictCompleteMe[\'öh, вау!\']',
I find it more readable to avoid escaped quotes whenever possible. Here I would use "DictCompleteMe['öh, вау!']".