Python is everywhere. Many core components of a modern distribution depend on it. In many times this fact makes difficult to upgrade Python to a version different from the distribution default. There are some alternatives, such as installing newer versions from source code, installing it in a different directory, or using third-party repository or PPAs then running update-alternatives. However, the latter approach often leads to problems, since we are changing the global Python version (i.e. the one used as default for the entire system). The former usually works, but you’ll need to deal with setting up virtualenvs and a bunch of environment variables.
If for any reason you use an older distribution, chances are that you also want to use a software like jupiter, numpy or TensorFlow that might ask for an updated Python version. You are in a dilemma: “if I update, I break the system, if not, I can’t use cool software out there.”
Enter Pyenv. It was developed to resolve that problem. You can install as many Python versions you want, and even use a particular version per directory (AKA application-specific environment). How cool is that?? I’ve adopted pyenv for about 6 months and I’m very happy with it.
I still use Ubuntu 16.04 LTS due to proprietary EDAs and related softwares I use in my work. So before adopting Pyenv I was somewhat stuck to Python versions 2.7.12 and 3.5.2. To run other, I used to use the virtualenv + environment variables approach. Not fun at all!!. I was often running into problems. Pyenv presents an elegant solution for these headaches.
We here go through the procedure to install Pyenv, Python 3.6.8 and Cocotb (at this time of writing, stable version 1.4.0). This isn’t a complete Pyenv reference. For such, I suggest you to visit this page to learn more.
Installing pyenv
This section describes how to install Pyenv for a non-root user. To complete this task you’ll need curl and git installed available in your system. Installation is as simple as:
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$ curl https://pyenv.run | bash
A ~/.pyenv directory will be created with a clone of its github repository. Then add the configuration printed out by the installer to your ~/.bashrc. Something like:
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export PATH="$HOME/.pyenv/bin:$PATH"
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
Finally, you may re-execute your shell:
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$ exec $SHELL
Then do a test by running pyenv.
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$ pyenv -v
pyenv 1.2.21
Before installing any Python
A few deb packages are recommended to be available in your system previous to installing Python for cocotb:
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$ sudo apt install build-essential libz-dev libssl-dev libsqlite3-dev libbz2-dev libreadline6-dev libffi-dev
Installing a Python for cocotb
Run the following command to list which Python versions you can install using Pyenv:
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$ pyenv install --list | less
For cocotb, I have installed version 3.8.6. But here is the catch. cocotb needs a Python built with --enable-shared option, which Pyenv doesn’t use by default. So, to correctly build and install Python under Pyenv, execute:
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$ PYTHON_CONFIGURE_OPTS="--enable-shared" pyenv install -v 3.8.6
You can check if version 3.8.6 was installed with:
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$ pyenv versions
* system (set by /home/lucas/.pyenv/version)
3.8.6
Setting up an application-specific environment
Here comes a pretty cool functionality provided by Pyenv. You can setup an application-specific Python environment. Each environment is contained within a directory. This means you can have as many Python versions you want. When you cd to a directory, Pyenv “automagically” sets the environment for that directory. This setup is accomplished by the pyenv local <VERSION> command.
Naturally we will setup an environment for cocotb. Let’s say that it will be in the ~/cocotb directory. Starting from user’s home directory, you’ll do:
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$ mkdir cocotb
$ cd cocotb
$ python -V
Python 2.7.12
$ pyenv local 3.8.6
$ python -V
Python 3.8.6
As you can see, Python 3.8.6 is enabled for the ~/cocotb directory.
Installing auxiliary Python packages
After Pyenv finishes the previous step, pip and setuptools are already available (current directory is ~/cocotb):
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$ pip list
Package Version
---------- -------
pip 20.2.1
setuptools 49.2.1
If a pip version warning shows up, you can update it with:
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$ python -m pip install --upgrade pip
However, you will need to install Python wheel as well:
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$ pip install wheel
$ pip list
Package Version
---------- -------
pip 20.2.4
setuptools 49.2.1
wheel 0.35.1
Installing cocotb
You may install cocotb in two ways. Using pip (easier) or using source code. Let’s go through both ways.
Using pip
Remember we still need to be in ~/cocotb. Just use pip to install cocotb. The latest stable version will be installed:
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$ pip install cocotb
$ pip list
Package Version
---------- -------
cocotb 1.4.0
pip 20.2.4
setuptools 49.2.1
wheel 0.35.1
Another cool thing is that cocotb-config will already be in your $PATH:
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$ cocotb-config --version
1.4.0
Very convenient, huh??
Now you can download cocotb examples and run.
From source code
Installing cocotb from source code is also very easy. We’ll use the repository in this example, however you can also use tarballs available at cocotb’s github repo.
Since we’ll be installing version 1.4.X, we will checkout stable/1.4 branch. Again, we are starting from ~/cocotb:
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$ git clone https://github.com/cocotb/cocotb.git cocotb-repo
$ cd cocotb-repo
$ git checkout stable/1.4
$ python setup.py install
Note that using the repository, you may be installing a version, say 1.4.1, which might not be available for installing using pip.
I hope Pyenv will be useful to you on running various Python systems as it was for me. I encourage you to try cocotb + Pyenv approach. Using both together has been very advantageous for sure!