import re


def elapsed(t1, t2):
    """
    Return a printable string showing the time elapsed from t1 to t2.
    """
    # Use the timedelta's standard formatting, except discard microseconds.
    retval = str(t2 - t1)
    m = re.match(r"([^.]+)\.([0-9]+)", retval)
    if m:
        retval = m.group(1)
    return retval