Install libraires on Ubuntu for Python3 and not Python2 [duplicate]

TL;DR

Each installed version of python have its own version of pip executable (at least for ubuntu), e.g. python2 have related pip2, python3 - pip3.

python and pip is just defaults which is simplinks to python2 or python3 binary.

So you can use

pip3 install <package> 

in most cases when you need to install package for python 3.

Lets find out how it works

pip is not binary!

Look at command for running pip python package, by executing following command:

$ less $(which pip)

Output will be something like this:

#!/usr/bin/python
# EASY-INSTALL-ENTRY-SCRIPT: 'pip==1.5.4','console_scripts','pip'
__requires__ = 'pip==1.5.4'
import sys
from pkg_resources import load_entry_point

if __name__ == '__main__':
    sys.exit(
        load_entry_point('pip==1.5.4', 'console_scripts', 'pip')()
    )

Actually, most of commands in linux aren't binaries. A lot of them just helpful bindings, just like in case with pip.

$ ls -lah $(which pip)
-rwxr-xr-x 1 root root 281 чер 17 00:52 /usr/bin/pip

You can find simple description of how executable scripts works on linux. It is written for bash scripts but applied for any interpreted language: python, javascript, ruby, etc.

So, if pip is not binary, then what does this script?

RTFM about pip, in few words, pip is just a python module and can be executed as any other python module, look at PEP 0338, e.g.

$ python -m pip install <package>

have same same effect as for command

$ pip install <package>

Summary

pip is python script that runs pip package with passed parameters. Package relative for python version in $ which pip file. If you will open your pip script, you will find for which python version it is related for.

In my case it is:

$ head -1 $(which pip)
#!/usr/bin/python
$ /usr/bin/python -V
Python 2.7.6

or oneliner

$ $(expr substr `head -1 $(which pip)` 3 100) -V
Python 2.7.6