error durring the bitcoincore installation I want to use python-OP_RETURN library. 
For this I need to install bitcoin core. 
But when I exceute this command
sudo apt-get update I have this error : 

Err http://ppa.launchpad.net jessie/main amd64 Packages                          

Err http://ppa.launchpad.net jessie/main amd64 Packages                          

Err http://ppa.launchpad.net jessie/main amd64 Packages      

Err http://ppa.launchpad.net jessie/main amd64 Packages                                                                   

Err http://ppa.launchpad.net jessie/main amd64 Packages                                                                   
  404  Not Found
Get:2 http://security.debian.org jessie/updates/main amd64 Packages [371 kB]                                         
Ign http://httpredir.debian.org jessie InRelease                                                                         
Get:3 http://httpredir.debian.org jessie-updates InRelease [142 kB]                       
Hit http://httpredir.debian.org jessie Release.gpg
Hit http://httpredir.debian.org jessie Release              
Get:4 http://httpredir.debian.org jessie-updates/main amd64 Packages [17.6 kB]
Get:5 http://httpredir.debian.org jessie/main amd64 Packages [9032 kB]
Fetched 9626 kB in 8s (1085 kB/s)                                                                                                                                                                                                          
W: Failed to fetch http://ppa.launchpad.net/bitcoin/bitcoin/ubuntu/dists/jessie/main/binary-amd64/Packages  404  Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.


What does it mean?
Your on debian the bitcoin PPA only works on ubuntu.
See this guide to build it on debian.
https://github.com/bitcoin/bitcoin/blob/master/doc/build-unix.md