The following signatures couldn'

apt-get update时报错:

Hit:1 http://mirrors.aliyun.com/ubuntu xenial InRelease
Hit:2 http://mirrors.aliyun.com/ubuntu xenial-updates InRelease                                                                                                                                                                           
Hit:3 http://mirrors.aliyun.com/ubuntu xenial-backports InRelease                                                                                                                                                                         
Hit:4 http://mirrors.aliyun.com/ubuntu xenial-security InRelease                                                                                                                      
Get:5 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu xenial InRelease [18.0 kB]                                                                                                       
Hit:6 http://archive.ubuntu.com/ubuntu xenial InRelease                                                                                   
Ign:5 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu xenial InRelease                                                                     
Hit:7 http://archive.canonical.com/ubuntu xenial InRelease                         
Fetched 18.0 kB in 1s (11.5 kB/s)                       
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net/deadsnakes/ppa/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BA6932366A755776
W: The repository 'http://ppa.launchpad.net/deadsnakes/ppa/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

执行下面的命令解决,其中BA6932366A755776与报错中的内容一致
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys BA6932366A755776