Set mirroring unusual problems arise, dpkg: warning: files list file for package. . .

1. Description of the problem, I set up Tsinghua mirror source accordance with the process online, but using sudo apt-get install python3-pip time command to install pip of an error. I'm prompted to use sudo apt --fix-broken install command, then use this command, error dpkg: warning: files list file for package. . . And then I found some cases way, delete files error, warning all to reinstall all files, and then can not solve the problem. After inadvertently also see a mirror source Tsinghua University, found my address and set up slightly different, so I reset the image address, the problem is resolved.
2. 这是我最后设置的清华源镜像，deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
       deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
       deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
       deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
       deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
       deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
       deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
       deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
       deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
       deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse。
3. Set mirror source method, sudo gedit /etc/apt/sources.list , then follow the prompts to enter your password. The new image replaces the source address of the address sources.list file, save and exit. Re-enter the command sudo apt-get update command, Weeks Enter sudo APT-GET upgrade , the problem is resolved.