Python Configuration in Ubuntu 21.04 or 21.10

Default python

python3 -V

In Ubuntu 21.04, the default Python installation are Python 3.9.4 and Python 2.7.18. They come with the Ubuntu installation and are located in /usr/bin/python. Because it usually requires special version of Python with different projects. It is always a good idea to install different versions of Python in the local.

Normal installation with Ubuntu.

Normally, it is very easy to install in Ubuntu. Follow this excellent page to do it. The method relies on a PPA ppa:deadsnakes/ppa. However, this PPA only support up to Ubuntu 20.10. Thus, we have to turn to install Python from resource. Here is a page that may work to use PPA on higher Ubuntu version. I have not tested it yet.

Install python3.8 from Resource

1. Install required packages for Python. Some of the following packages might be missing and cannot be installed. Just delete the missing packages.

   $ sudo apt-get install libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev build-essential libreadline-dev libffi-dev zlib1g-dev liblzma-dev lzma
   

2. Download the *.tgz from the resource.
3. Navigate to the downloaded place and use the following command to unzip the file. tar xf Python-3.8.9.tgz
4. Navigate to the unzipped folder by using cd Python-3.8.9 and run the configuration file ./configure
5. Use the following commands to install Python 3.8. Please make sure use sudo make. I have tried make and sudo make install. It turns out that Python3.8 can be installed but I cannot use pip after the installation. The error code is pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available. I have no idea why it happens. I have tried to follow this page to install a new openssl in usr/local/bin. But it does NOT help.

   $ sudo make && sudo make install
   

6. Now python is installed in usr/local/bin. It will overwrite the default Python 3.9.4 and runs as default.

   $ python3 -V
   

Package LZMA Missing

After installing from resource, it can have an error showing ModuleNotFoundError: No module named '_lzma'. This can be due to that the installation is from source and incomplete. To solve this problem, follow this discussion. A complete solution is to install liblzma-dev and lzma using sudo apt-get install. Afterwards, re-install the python package. The complete code is as follows:

$ sudo apt-get install liblzma-dev
$ sudo apt-get install lzma
$ tar xf Python-3.8.12.tgz
$ cd Python-3.8.12/
$ ./configure
$ sudo make && sudo make install

Use Python built-in venv to manage virtual environments

Use the default python

If using python3, will use the default python to create a virtual environment.

$ python3 -m venv test_env
$ cd /test_env
$ source bin/activate

Use another version of python

You can specify a specific version of python that you want to use in the virtual environment.

$ python3.9 -m venv test_env2
$ cd /test_env2
$ source bin/activate

Use Virtualenv to configure the virtual development environment.

$ mkdir test_py
$ cd test_py/
$ virtualenv --python=/usr/local/bin/python3.8 py_38_env

py_38_env is the virtual environment name. Use source py_38_test/bin/activate to activate the virtual environment. Use deactivate to exit the virtual environment.

Useful links

The following links are useful.

1. Tutorial about how to install a package from resource. link.
2. Solving the pip problem. link

Remove the installation files from download

cd ~/Downloads/
rm Python-3.8.9.tgz
sudo rm -r Python-3.8.9