how to use python2.7 pip instead of default pip

There should be a binary called "pip2.7" installed at some location included within your $PATH variable.

You can find that out by typing

which pip2.7

This should print something like '/usr/local/bin/pip2.7' to your stdout. If it does not print anything like this, it is not installed. In that case, install it by running

$ wget https://bootstrap.pypa.io/pip/2.7/get-pip.py
$ sudo python2.7 get-pip.py

Now, you should be all set, and

which pip2.7

should return the correct output.

An alternative is to call the pip module by using python2.7, as below:

python2.7 -m pip <commands>

For example, you could run python2.7 -m pip install <package> to install your favorite python modules. Here is a reference: https://stackoverflow.com/a/50017310/4256346.

In case the pip module has not yet been installed for this version of python, you can run the following:

python2.7 -m ensurepip

Running this command will "bootstrap the pip installer". Note that running this may require administrative privileges (i.e. sudo). Here is a reference: https://docs.python.org/2.7/library/ensurepip.html and another reference https://stackoverflow.com/a/46631019/4256346.

as noted here, this is what worked best for me:

sudo apt-get install python3 python3-pip python3-setuptools

sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 10