Configuring Python

Versions supported

The default version can be changed from the alwaysdata administration, under Environment > Python. This is the version that is especially used when you start python.

Error logs

You can view the error logs in the $HOME/admin/logs/uwsgi/[id].log file where [id] is the identifier for your site, shown in the Web > Sites section.

Binary to use

You need to always use python (or /usr/bin/python). Never use python3, python2, python2.7 or any other command.

To force the use of a different version of Python other than the default one, define the environment variable PHYTHON_VERSION:

$ PYTHON_VERSION=2.7 python

In your scripts, use /usr/bin/python as shebang:

#!/usr/bin/python

To force the use of a specific version of Python:

#!/usr/bin/eval PYTHON_VERSION=2.7 python

The other binaries included in Python (2to3, pep8, pip, pydoc, etc.) work the same way.

Environment

Your Python environment starts off empty, with no ready installed libraries other than the standard library. You can use pip to install packages, this is the standard Python tool:

$ pip install Django

Packages are installed in the standard $HOME/.local directory and they are automatically added to sys.path by Python.

Note that you will need to re-install the packages if you change the major Python version (versions 3.5 and 3.6 are two different major versions, whereas 3.5.1 and 3.5.2 use the same major version).

We recommend using virtual environments if you use a number of different Python applications so that each one has its own separate environment.

With Python 3, use venv:

$ python -m venv myenv

With Python 2, use virtualenv:

$ virtualenv myenv

Once your virtual environment is installed, you can activate it with:

$ source myenv/bin/activate

Installing a package

Install the latest version of a package:

$ pip install Django

You can specify a specific version:

$ pip install Django==1.10.4

To install a set of packages defined in a requirements.txt file:

$ pip install -r requirements.txt

Uninstalling a package

$ pip uninstall Django

Installing a package with Distutils

You can install a package using Distutils without using pip:

$ python setup.py install --user

If you use a virtual environment, there is no need to specify --user.

WSGI deployment

So that a WSGI application is accessible by the web, you need to add a site in the administration Web > Sites section:

• type: choose Python WSGI,
• application path: the path to your WSGI application.

You can also fill-in a number of optional fields:

• your application’s working directory,
• environment variables to define,
• a specific version of Python to use,
• the virtualenv directory to use.