how can i use pip with pypy installed from launchpad?

Quoting (with minor changes) from here the pypy website:

If you want to install 3rd party libraries, the most convenient way is
to install pip:

$ curl -O https://bootstrap.pypa.io/get-pip.py
$ ./pypy-2.1/bin/pypy get-pip.py
$ ./pypy-2.1/bin/pip install pygments  # for example

In order to use it nicely, you might want to add an alias into e.g. ~/.bashrc:

alias pypy_pip='./pypy-2.1/bin/pip'

Where the actual pip executable is located has to be taken from the output of pypy get-pip.py