[Python-Dev] pathlib - current status of discussions (original) (raw)

Stephen J. Turnbull stephen at xemacs.org
Tue Apr 12 01:28:51 EDT 2016

Donald Stufft writes:

I think yes and yes [fspath and fspath should be allowed to handle bytes, otherwise] it seems like making it needlessly harder to deal with a bytes path

It's not needless. This kind of polymorphism makes it hard to review code locally. Once bytes get a foothold inside a text application, they metastasize altogether too easily, and you end up with TypeErrors or UnicodeErrors quite far from the origin. Debugging often requires tracing data flows over hill and over dale while choking from the dusty trail, or band-aids like a top-level "except UnicodeError: log_and_quarantine(bytes)". I can't prove that returning bytes from these APIs is a big risk in this sense, but I can't see a way to prove that it's not, either, given that their point is duck-typing, and therefore they may be generalized in the future, and by third parties.

I understand that there are applications where it's bytes all the way down, but by the very nature of computing systems, there are systems where bytes are decoded to text. For historical reasons (the encoding Tower of Babel), it's very error-prone to do that on demand. Best practice is to do the conversion as close to the boundary as possible, and process only text internally.

In text applications, "bytes as carcinogen" is an apt metaphor.

Now, I'm not Dutch, so I can't tell you it's obvious that the risk to text-processing applications is more important than the inconvenience to byte-shoveling applications. But there is a need to be parsimonious with polymorphism.

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