Parse accept headers.

def parse_accept_header(header):
    """Parse accept headers."""
    result = []
    for match in accept_re.finditer(header):
        quality = match.group(2)
        if not quality:
            quality = 1
        else:
            quality = max(min(float(quality), 1), 0)
        result.append((match.group(1), quality))
    return result