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Python Configuration in Ubuntu 21.04 or 21.10

·578 words·3 mins
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Default python
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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.
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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
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  1. Install required packages for Python. Some of the following packages might be missing and cannot be installed. Just delete the missing packages.
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    $ 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.
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    $ 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.
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    $ python3 -V

Package LZMA Missing
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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:

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

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

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

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

Use Virtualenv to configure the virtual development environment.
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$ 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
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cd ~/Downloads/
rm Python-3.8.9.tgz
sudo rm -r Python-3.8.9