[JackC]

I'll add "reduce code size and complexity" to the list of benefits. A python library to calculate a simhash, or track changes on a django model, or auto generate test fixtures, will often be 90% configuration cruft for other usecases, and 10% the code your app actually cares about. Reading the library and extracting and finetuning the core logic makes you responsible for the bugs in the 10%, but no longer affected by bugs in the 90%.

[dkarl]

Hard agree. A library should not inflict complex use cases' complexity on simple use cases, but sometimes they do, either because they're poorly designed or because they're overkill for your use case. But often I see pain and complexity excused with "this is the library that everybody else uses."

Sometimes a simple bespoke solution minimizes costs compared to the complexity of using a massive hairball with a ton of power that you don't need.

One big caveat to this: there's a tendency to underestimate the cost and complexity of a solution that you, personally, developed. If new developers coming onto the project disagree, they're probably right.

[jofer]

The big caveat is a big one. Choose your battles wisely!

There are plenty of things that look simpler than an established library at first glance (I/O of specialized formats comes to mind quickly). However, a lot of the complexity of that established library can wind up being edge cases that you actually _do_ care about, you just don't realize it yet.

It's easy to wind up blind to maintenance burden of "just a quick add to the in-house version" repeated over and over again until you wind up with something that has all of the complexities of the widely used library you were trying to avoid.

With that said, I still agree that it's good to write things from scratch and avoid complex dependencies where possible! I just think choosing the right cases to do so can be a bit of an art. It's a good one to hone.

[geysersam]

At my current workplace the word "bespoke" is used to mean anything that is "business logic" and everyone are very much discouraged from working on such things. On the other hand we've got a fantastic set of home made tooling and libraries, all impressive software engineering, almost as good as the of the shelf alternatives.