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Using Python 3 on CentOS 7 (the easy way)

Whether you’re running Sopel, or any other Python application, the best way to install Python 3 on CentOS 7 is with Software Collection Libraries. Many guides will tell you to compile it, but that’s much more time consuming, makes you mess with your path, and can’t be kept up to date with yum. SCL is a much more elegant solution, and all you need to do is this1:

yum install scl-utils
yum install rhscl-python33-*.noarch.rpm
yum install python33
easy_install pip

You can then enable it for a command by putting scl enable python33 before it. If you want to run your shell, do scl enable python33 -- $SHELL. 2 If you want the Python REPL, scl enable python33 -- python.

pip is not included (outside of virtualenv, which is included). To install it, do easy_install pip with the SCL active. Then, with it still active, you can pip install sopel (or whatever other package you want).

Using SCL in systemd services

If you’re already familiar with systemd, it should be clear what to do. Prepend all the commands in your unit file with /usr/bin/scl enable python33 --. The ExecStart in Sopel’s service file, when modified to use SCL, becomes this:

ExecStart=/usr/bin/scl enable python33 -- sopel -c /etc/sopel.cfg --quiet

1: If you’re looking to set this up on CentOS 6 or Fedora, the URL for wget will be different. See this page for the URL for your system.

2: The -- separates the arguments to SCL from your command. If you aren’t passing any arguments to your command, you can leave it out. But the error message when you forget it isn’t always straightforward, so it’s a good habit.