Chapter 23: Foundation Before Features — Pyenv, Poetry, and Venv, Part 1

1. Why Version Management Matters in Network Engineering

If you’ve been automating networks for more than a year, you’ve probably run headfirst into a silent but brutal problem: Python version chaos. Unlike writing code for a single application with a fixed set of requirements, network automation forces you to work across multiple vendors, multiple ecosystems, and multiple lifecycles all at once. Each vendor has its quirks, each SDK is pinned to different versions, and the operational environments you inherit rarely match the pristine documentation.

Take this real-world scenario: you’re building a Junos automation script ncclient to handle NETCONF operations. The library maintainers have already shifted to requiring Python 3.11 for the latest features and bug fixes. On the same week, you’re troubleshooting a lab script against another vendor pyeapi, which was certified only up to Python 3.9. Both tasks are critical. Both tasks land on your desk. And both tasks assume that “your Python” is precisely the one they were designed for.

Now imagine the third layer: production Ansible playbooks. These are the lifeblood of your operational workflows, tested and blessed for Python 3.9 in production because the enterprise automation platform hasn’t yet moved forward. Break compatibility here, and your production network configuration pipelines grind to a halt. Meanwhile, your experimental side-project with Nornir requires cutting-edge libraries that have already dropped support for anything older than Python 3.10.

This is the nightmare network engineers quietly live with. On your laptop, jump host, or shared automation server, these worlds collide into the infamous “dependency hell.” You try to upgrade Python for one project and immediately break another. You attempt to install a library globally, and suddenly your Ansible playbooks fail on a production change window. The problem isn’t your code; it’s the environment in which your code runs.

And this is where Pyenv steps in. Unlike generic software developers who may run a single monolithic web app, network engineers routinely juggle dozens of scripts, frameworks, and vendor SDKs. Each of them ties to a specific Python runtime. Pyenv provides a clean, reliable way to install and switch between these runtimes. It’s like having a routing policy for your interpreters: you decide which Python version applies to which project, and you enforce that policy with precision.

Without this discipline, automation quickly devolves into firefighting. You’ll spend more time trying to reconcile Python versions than writing the automation logic that should actually deliver business value. With Pyenv, you get back the one thing every network engineer craves: control. Control over the interpreter, control over the dependencies, and control over the outcome.

That’s why version management matters in network engineering. It isn’t about keeping your workstation tidy but instead building a foundation stable enough to support the complex, multi-vendor, multi-tool pipelines that define modern network automation.

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