import re


def extract_timestamp(line):
    """Extract timestamp from log item.

    :param line: log item.
    :type line: str
    :return: timestamp or empty string
    :rtype: str
    """
    rex = r"(\d{4}\-\d\d\-\d\d\s\d\d:\d\d:\d\d[\,\d]*[\s\w]*)"
    match = re.search(rex, line)
    if match:
        return match.group(1)
    return ""