For Ubuntu 18.04 with python 3.6.5 the python-pip package will install after :

sudo add-apt-repository universe
sudo apt-get update

Which is enabling the category universe

deb  bionic main universe
deb  bionic-security main universe 
deb  bionic-updates main universe

Following a clean install of Ubuntu 18.04 (via Vagrant) the following installed successfully with no issues:

  sudo apt-get update
  sudo apt-get install -y python3-pip

Note that the Ubuntu 18.04 download today shipped with Python 3.6.8 installed. This may vary by the time of your reading this post.

First update then install python3-pip.So following two commands should work.

sudo add-apt-repository universe
sudo apt-get update
sudo apt-get install python3-pip

first run sudo apt-get upgrade if you see ppa:some repository example launchpad.net not found or ip not found then go to

softwares&update then unmark repository's causing error then select ubuntu main server then reload and run command sudo apt-get update sudo apt-get autoremove sudo apt-get autoclean it will delete unwanted existing packages and clear cache then try

sudo apt-get update
sudo apt-get install -y python3-pip

These commands work for me -

sudo apt-get install python3-setuptools
sudo easy_install3 pip

This is the old way of installing pip especially useful for the old version of Ubuntu. But still works fine for me.

you have to clear the unwanted repository's code /etc/apt/sources.list or gedit /etc/apt/sources.list or another option is switch ubuntu mirror see how to change ubuntu mirror

sudo apt-get update; sudo apt-get install python3-pip;

The other way is adding universe category into current sources.list directly:

vi /etc/apt/sources.list

Then add universe category at the end of each line:

deb  bionic main universe
deb  bionic-security main universe
deb  bionic-updates main universe