[Python Dependency Pitfalls] How to set the world on fire

Hey there,

#1 on my list of dependency management pitfalls is there for a good reason:

It lead to a single developer causing mayhem and breaking thousands of open-source projects around the world in one fell swoop.

Here's how it all went down:

A few years back, Azer Koçulu wrote a tiny library he published on Npm, the package repository for NodeJS. (The Python equivalents would be PyPI + pip.)

That "library" contained only 11 lines of code in total, but it was downloaded MILLIONS of times every month of as a dependency in other JavaScript projects.

What Azer's magical "micro library" did, you ask?

It added a tiny piece of functionality that was frequently needed but wasn't a part of the NodeJS standard library:

The ability to pad out the lefthand-side of strings with zeroes or spaces. For example, to format numbers for display.

In Python you'd probably do something like this:

>>> n = '4'
>>> n.zfill(3)
'004'

Anyway, this tiny "left-pad" library was used across many projects, including important applications like Node itself.

One fine day, Azer decided to close his NodeJS package repository account…

Which removed all of the packages associated with it.

And suddenly, "left-pad" was no longer available for download…

Can you guess what happened to the dependency install setup steps on projects using "left-pad?"

Well, they came to a SCREECHING HALT:

App deployments became stuck dead in their tracks. Automated tests stopped working.

And thousands of developers couldn't even RUN their apps locally…

All because "left-pad" had disappeared—and some important build tools required it to work.

It was quite crazy. Even some newspapers reported about the "left-pad incident."

You can imagine that there was a lot of "bruhaha" about the NodeJS packaging system—

But to tell you the truth the *exact same thing* could happen at any time with Python's packaging repository, PyPI.

It's easy to think that pulling in functionality from 3rd party dependencies is always a net benefit.

But every time you're adding an external dependency to your own project you're walking a fine line…

BAD external dependencies can make your stomach churn as a developer or project maintainer.

The people who got burned by the NodeJS "left-pad" incident know what I'm talking about...

On the other hand, a great quality third-party package can save you hours or even days of work.

The challenge is deciding whether a dependency adds value or is just a liability:

>> See step-by-step how to research and make Python dependency decisions (and how to explain them to your team/manager)

— Dan Bader

P.S. There's an important skill that Python dev managers look for in a candidate, but they rarely find it. More on that tomorrow.