def find_start_of_previous_word(self, count=1, WORD=False):
        """
        Return an index relative to the cursor position pointing to the start
        of the previous word. Return `None` if nothing was found.
        """
        # Reverse the text before the cursor, in order to do an efficient
        # backwards search.
        text_before_cursor = self.text_before_cursor[::-1]

        regex = _FIND_BIG_WORD_RE if WORD else _FIND_WORD_RE
        iterator = regex.finditer(text_before_cursor)

        try:
            for i, match in enumerate(iterator):
                if i + 1 == count:
                    return - match.end(1)
        except __HOLE__:
            pass
dataset/ETHPy150Open jonathanslenders/python-prompt-toolkit/prompt_toolkit/document.py/Document.find_start_of_previous_word