Hi Marcus ,thank you for your reply .
gr-eventstream just insert zero to output and can't be useful in this case , i need something like this block :
https://github.com/drmpeg/gr-mpeIn gr-mpe block if there are no packet in TUNTAP it produce null packet to satisfy output rate , i need do same sing in python block .
Are there any documentation available for doing some thing similar with python blocks ?
Is that even possible ?