def _make_serializer(meas, schema, rm_none, extra_tags, placeholder):
    _validate_schema(schema, placeholder)
    tags = []
    fields = []
    ts = None
    meas = meas
    for k, t in schema.items():
        if t is MEASUREMENT:
            meas = f"{{i.{k}}}"
        elif t is TIMEINT:
            ts = f"{{i.{k}}}"
        elif t is TIMESTR:
            if pd:
                ts = f"{{pd.Timestamp(i.{k} or 0).value}}"
            else:
                ts = f"{{dt_to_int(str_to_dt(i.{k}))}}"
        elif t is TIMEDT:
            if pd:
                ts = f"{{pd.Timestamp(i.{k} or 0).value}}"
            else:
                ts = f"{{dt_to_int(i.{k})}}"
        elif t is TAG:
            tags.append(f"{k}={{str(i.{k}).translate(tag_escape)}}")
        elif t is TAGENUM:
            tags.append(f"{k}={{getattr(i.{k}, 'name', i.{k} or None)}}")
        elif t in (FLOAT, BOOL):
            fields.append(f"{k}={{i.{k}}}")
        elif t is INT:
            fields.append(f"{k}={{i.{k}}}i")
        elif t is STR:
            fields.append(f"{k}=\\\"{{str(i.{k}).translate(str_escape)}}\\\"")
        elif t is ENUM:
            fields.append(f"{k}=\\\"{{getattr(i.{k}, 'name', i.{k} or None)}}\\\"")
        else:
            raise SchemaError(f"Invalid attribute type {k!r}: {t!r}")
    extra_tags = extra_tags or {}
    for k, v in extra_tags.items():
        tags.append(f"{k}={v}")
    if placeholder:
        fields.insert(0, f"_=true")
    sep = ',' if tags else ''
    ts = f' {ts}' if ts else ''
    fmt = f"{meas}{sep}{','.join(tags)} {','.join(fields)}{ts}"
    if rm_none:
        pat = r',\w+="?None"?i?'
        f = eval('lambda i: re.sub(r\'{}\', "", f"{}").encode()'.format(pat, fmt))
    else:
        f = eval('lambda i: f"{}".encode()'.format(fmt))
    f.__doc__ = "Returns InfluxDB line protocol representation of user-defined class"
    f._args = dict(meas=meas, schema=schema, rm_none=rm_none,
                   extra_tags=extra_tags, placeholder=placeholder)
    return f