Hello,
Python 3.7 removes the undocumented internal import `os.errno`.
We consider that a an implementation detail, which can be changed
*without notice* even in a bugfix release. Projects that depend on it
are incorrect and should be fixed.
On bpo-33666, there's a debate on whether the removal should be
mentioned in release notes, on the grounds that it broke some projects,
is used in quire a few tutorials/books/examples, and it's been working
since Python 2.5 or so.
But here's the thing: the more I think about this, the less I consider
`os.errno` as "undocumented". Here's what I consider a reasonable path a
programmer might go through:
# Where do I find errno values?
# Maybe it's in `os`, like all other basic platform bindings?
>>> import os
>>> os.err<tab>
os.errno os.error(
>>> help(os.errno)
Help on built-in module errno:
...
# Yup, There it is!
Even more serious:
# Hmm, this old example on some website tells me to use `os.errno`.
# It's the first time I'm hear about that, so I'll be extra careful;
>>> import os
>>> os.errno
<module 'errno' (built-in)>
# Yup, it's there! Let's double-check the docs.
>>> help(os.errno)
Help on built-in module errno:
...
# Yup, looks quite alright! Let's use it!
As you can see, the built-in documentation does not contain *any*
warnings against using `os.errno`.
You might think the fact that it's called "errno" and not "os.errno" is
a red flag, but it's not, really -- "os.path" is (on my system) named
"posixpath", yet "os.path" is the name to use.
While most people might prefer searching docs.python org to `help()`,
editors are getting better and better to presenting introspection and
the built-in docs, so more and more people are preferring `pydoc`-ish
docs to going online.
I don't think we can reasonably expect people who used built-in help as
above to go back and check that Python's official docs *do not* contain
`os.errno`. Effectively, while `os.errno` is not very *discoverable*
using official docs alone, I don't think calling it *undocumented* is fair.
So, removing it without notice is not very friendly to our users.
Is that reasoning sound?
Should our policy on removing internal imports take that into account?
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