description implementation

some of the description fields are incorrect :

• display_size : currently return max_length, but for string must return the real display length : max length / collation byte per character
• precision : must be calculate for decimal according to length and scale : +1 if signed, + 1 if have scale (i.e : 123.45 has a precision of 5 and a scale of 2, and a length of 7)

And ... why this 8th field to return flag, since PEP249 indicate having 7 fields (https://www.python.org/dev/peps/pep-0249/#description) ?