Tab completions may be suffixed with ' ' (keywords), ':' (keywords)*, or '(' (callables) if one of those is required. Ex. 'import ', 'finally:', 'len('. Attributes may get '('. The possible downside is needing to remove the suffix if one does not want the completion for what it is but as a prefix to a longer word. Ex. 'imports','elsewhere', 'length'. But this should be much less common in code.
* 'else ' should be 'else:'
With keywords added (#37765) tab list is sorted(Completer().global_match('') + list(__main__.dict__.keys())). Whatever decide on, calculate first part once (if not already). list.sort used preexisting order. key are sorted. builtins might be.