Convenience method for conditional requests.

    :param environ: the WSGI environment of the request to be checked.
    :param etag: the etag for the response for comparison.
    :param data: or alternatively the data of the response to automatically
                 generate an etag using :func:`generate_etag`.
    :param last_modified: an optional date of the last modification.
    :param ignore_if_range: If `False`, `If-Range` header will be taken into
                            account.
    :return: `True` if the resource was modified, otherwise `False`.

def is_resource_modified(
    environ, etag=None, data=None, last_modified=None, ignore_if_range=True
):
    """Convenience method for conditional requests.

    :param environ: the WSGI environment of the request to be checked.
    :param etag: the etag for the response for comparison.
    :param data: or alternatively the data of the response to automatically
                 generate an etag using :func:`generate_etag`.
    :param last_modified: an optional date of the last modification.
    :param ignore_if_range: If `False`, `If-Range` header will be taken into
                            account.
    :return: `True` if the resource was modified, otherwise `False`.
    """
    if etag is None and data is not None:
        etag = generate_etag(data)
    elif data is not None:
        raise TypeError("both data and etag given")
    if environ["REQUEST_METHOD"] not in ("GET", "HEAD"):
        return False

    unmodified = False
    if isinstance(last_modified, string_types):
        last_modified = parse_date(last_modified)

    # ensure that microsecond is zero because the HTTP spec does not transmit
    # that either and we might have some false positives.  See issue #39
    if last_modified is not None:
        last_modified = last_modified.replace(microsecond=0)

    if_range = None
    if not ignore_if_range and "HTTP_RANGE" in environ:
        # https://tools.ietf.org/html/rfc7233#section-3.2
        # A server MUST ignore an If-Range header field received in a request
        # that does not contain a Range header field.
        if_range = parse_if_range_header(environ.get("HTTP_IF_RANGE"))

    if if_range is not None and if_range.date is not None:
        modified_since = if_range.date
    else:
        modified_since = parse_date(environ.get("HTTP_IF_MODIFIED_SINCE"))

    if modified_since and last_modified and last_modified <= modified_since:
        unmodified = True

    if etag:
        etag, _ = unquote_etag(etag)
        if if_range is not None and if_range.etag is not None:
            unmodified = parse_etags(if_range.etag).contains(etag)
        else:
            if_none_match = parse_etags(environ.get("HTTP_IF_NONE_MATCH"))
            if if_none_match:
                # https://tools.ietf.org/html/rfc7232#section-3.2
                # "A recipient MUST use the weak comparison function when comparing
                # entity-tags for If-None-Match"
                unmodified = if_none_match.contains_weak(etag)

            # https://tools.ietf.org/html/rfc7232#section-3.1
            # "Origin server MUST use the strong comparison function when
            # comparing entity-tags for If-Match"
            if_match = parse_etags(environ.get("HTTP_IF_MATCH"))
            if if_match:
                unmodified = not if_match.is_strong(etag)

    return not unmodified