<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _format_int(format, subtype, endian):
 """Return numeric ID for given format|subtype|endian combo."""

    result = _check_format(format)
    if subtype is None:
        subtype = default_subtype(format)
        if subtype is None:
            raise TypeError(
                "No default subtype for major format {0!r}".format(format))
    elif not isinstance(subtype, (_unicode, str)):
        raise TypeError("Invalid subtype: {0!r}".format(subtype))
    try:
        result |= _subtypes[subtype.upper()]
    except KeyError:
        raise ValueError("Unknown subtype: {0!r}".format(subtype))
    if endian is None:
        endian = 'FILE'
    elif not isinstance(endian, (_unicode, str)):
        raise TypeError("Invalid endian-ness: {0!r}".format(endian))
    try:
        result |= _endians[endian.upper()]
    except KeyError:
        raise ValueError("Unknown endian-ness: {0!r}".format(endian))

    info = _ffi.new("SF_INFO*")
    info.format = result
    info.channels = 1
    if _snd.sf_format_check(info) == _snd.SF_FALSE:
        raise ValueError(
            "Invalid combination of format, subtype and endian")
    return result