Method _guess_quote_and_delimiter

Lib/csv.py:272–346

Looks for text enclosed between two identical quotes (the probable quotechar) which are preceded and followed by the same character (the probable delimiter). For example: ,'some text', The quote with the most wins, same with the delim

(self, data, delimiters)

    def _guess_quote_and_delimiter(self, data, delimiters):
        """
        Looks for text enclosed between two identical quotes
        (the probable quotechar) which are preceded and followed
        by the same character (the probable delimiter).
        For example:
                         ,'some text',
        The quote with the most wins, same with the delimiter.
        If there is no quotechar the delimiter can't be determined
        this way.
        """
        import re

        matches = []
        for restr in (r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?P=delim)', # ,".*?",
                      r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?P<delim>[^\w\n"\'])(?P<space> ?)',   #  ".*?",
                      r'(?P<delim>[^\w\n"\'])(?P<space> ?)(?P<quote>["\']).*?(?P=quote)(?:$|\n)',   # ,".*?"
                      r'(?:^|\n)(?P<quote>["\']).*?(?P=quote)(?:$|\n)&#x27;):                            #  ".*?" (no delim, no space)
            regexp = re.compile(restr, re.DOTALL | re.MULTILINE)
            matches = regexp.findall(data)
            if matches:
                break

        if not matches:
            # (quotechar, doublequote, delimiter, skipinitialspace)
            return ('', False, None, 0)
        quotes = {}
        delims = {}
        spaces = 0
        groupindex = regexp.groupindex
        for m in matches:
            n = groupindex['quote'] - 1
            key = m[n]
            if key:
                quotes[key] = quotes.get(key, 0) + 1
            try:
                n = groupindex['delim'] - 1
                key = m[n]
            except KeyError:
                continue
            if key and (delimiters is None or key in delimiters):
                delims[key] = delims.get(key, 0) + 1
            try:
                n = groupindex['space'] - 1
            except KeyError:
                continue
            if m[n]:
                spaces += 1

        quotechar = max(quotes, key=quotes.get)

        if delims:
            delim = max(delims, key=delims.get)
            skipinitialspace = delims[delim] == spaces
            if delim == '\n': # most likely a file with a single column
                delim = ''
        else:
            # there is *no* delimiter, it's a single column of quoted data