import re


def find_matched_pos(str, pattern):
    """ Find all positions (start,end) of matched characters
    >>> find_matched_pos('ss12as34cdf', '\d')
    [(2, 3), (3, 4), (6, 7), (7, 8)]
    """
    match_objs = re.finditer(pattern ,str)
    match_pos = [match_obj.span() for match_obj in match_objs]

    return match_pos