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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _complete(self):
 """ Main completion function. Gets list of potential completion candidates for currently edited word, completes it to the longest common part, and shows convenient completion widget (if multiple completions are returned) with currently selected candidate highlighted. """

        def find_word_start(p_text, p_pos):
            """ Returns position of the beginning of a word ending in p_pos. """
            return p_text.lstrip().rfind(' ', 0, p_pos) + 1

        def get_word_before_pos(p_text, p_pos):
            start = find_word_start(p_text, p_pos)

            return (p_text[start:p_pos], start)

        pos = self.edit_pos
        text = self.edit_text
        completer = self.completer

        word_before_cursor, start = get_word_before_pos(text, pos)
        completions = completer.get_completions(word_before_cursor, start == 0)
        # store slices before and after place for completion
        self._surrounding_text = (text[:start], text[pos:])

        single_completion = len(completions) == 1
        completion_done = single_completion and completions[0] == word_before_cursor

        if completion_done or not completions:
            self.completion_mode = False
            return
        elif single_completion:
            replacement = completions[0]
        else:
            replacement = commonprefix(completions)
            zero_candidate = replacement if replacement else word_before_cursor

            if zero_candidate != completions[0]:
                completions.insert(0, zero_candidate)

            self.completion_box.add_completions(completions)

        self.insert_completion(replacement)
        self.completion_mode = not single_completion