def get_cov(pileup, raise_error_if_0x=False):
    """Returns the sum of matches + mismatches for a position.

    Optionally raises an error if this particular pileup has a 
    (match + mismatch) coverage of 0. (The error will also come up
    if through some twist of fate this pileup has a coverage of less
    than 0. If that happens, ...try calling an exorcist?)
    """
    cov = sum(pileup[0])
    if raise_error_if_0x and cov <= 0:
        raise ValueError(f"pileup {pileup} has coverage of {cov}x.")
    else:
        return cov