[python-3.x] How to install pip for Python 3.6 on Ubuntu 16.10?

I'd like to start by pointing out that this question may seem like a duplicate, but it isn't. All the questions I saw here were regarding pip for Python 3 and I'm talking about Python 3.6. The steps used back then don't work for Python 3.6.

1. I got a clear Ubuntu 16.10 image from the official docker store.
2. Run apt-get update
3. Run apt-get install python3.6
4. Run apt-get install python3-pip
5. Run pip3 install requests bs4
6. Run python3.6 script.py

Got ModuleNotFoundError below:

 Traceback (most recent call last):
    File "script.py", line 6, in <module>
     import requests
 ModuleNotFoundError: No module named 'requests'

Python's and pip's I have in the machine:

python3
python3.5
python3.5m
python3.6
python3m
python3-config
python3.5-config
python3.5m-config
python3.6m
python3m-config  

pip
pip3
pip3.5

This website contains a much cleaner solution, it leaves pip intact as-well and one can easily switch between 3.5 and 3.6 and then whenever 3.7 is released.

http://ubuntuhandbook.org/index.php/2017/07/install-python-3-6-1-in-ubuntu-16-04-lts/

A short summary:

sudo apt-get install python python-pip python3 python3-pip
sudo add-apt-repository ppa:jonathonf/python-3.6
sudo apt-get update
sudo apt-get install python3.6
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.5 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 2

Then

$ pip -V
pip 8.1.1 from /usr/lib/python2.7/dist-packages (python 2.7)
$ pip3 -V
pip 8.1.1 from /usr/local/lib/python3.5/dist-packages (python 3.5)

Then to select python 3.6 run

sudo update-alternatives --config python3

and select '2'. Then

$ pip3 -V
pip 8.1.1 from /usr/local/lib/python3.6/dist-packages (python 3.6)

To update pip select the desired version and

pip3 install --upgrade pip

$ pip3 -V
pip 9.0.1 from /usr/local/lib/python3.6/dist-packages (python 3.6)

Tested on Ubuntu 16.04.

This answer assumes that you have python3.6 installed. For python3.7, replace 3.6 with 3.7. For python3.8, replace 3.6 with 3.8, but it may also first require the python3.8-distutils package.

Installation with sudo

With regard to installing pip, using curl (instead of wget) avoids writing the file to disk.

curl https://bootstrap.pypa.io/get-pip.py | sudo -H python3.6

The -H flag is evidently necessary with sudo in order to prevent errors such as the following when installing pip for an updated python interpreter:

The directory '/home/someuser/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.

The directory '/home/someuser/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.

Installation without sudo

curl https://bootstrap.pypa.io/get-pip.py | python3.6 - --user

This may sometimes give a warning such as:

WARNING: The script wheel is installed in '/home/ubuntu/.local/bin' which is not on PATH. Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.

Verification

After this, pip, pip3, and pip3.6 can all be expected to point to the same target:

$ (pip -V && pip3 -V && pip3.6 -V) | uniq
pip 18.0 from /usr/local/lib/python3.6/dist-packages (python 3.6)

Of course you can alternatively use python3.6 -m pip as well.

$ python3.6 -m pip -V
pip 18.0 from /usr/local/lib/python3.6/dist-packages (python 3.6)

In at least in ubuntu 16.10, the default python3 is python3.5. As such, all of the python3-X packages will be installed for python3.5 and not for python3.6.

You can verify this by checking the shebang of pip3:

$ head -n1 $(which pip3)
#!/usr/bin/python3

Fortunately, the pip installed by the python3-pip package is installed into the "shared" /usr/lib/python3/dist-packages such that python3.6 can also take advantage of it.

You can install packages for python3.6 by doing:

python3.6 -m pip install ...

For example:

$ python3.6 -m pip install requests
$ python3.6 -c 'import requests; print(requests.__file__)'
/usr/local/lib/python3.6/dist-packages/requests/__init__.py