[Python-Dev] Breaking undocumented API (original) (raw)

Tres Seaver tseaver at palladion.com
Wed Nov 10 17:58:17 CET 2010

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On 11/09/2010 11:12 PM, Stephen J. Turnbull wrote:

Nick Coghlan writes:

> > Module writers who compound the error by expecting to be imported > > this way, thereby bogarting the global namespace for their own > > purposes, should be fish-slapped. ;) > > Be prepared to fish-slap all of python-dev then - we use precisely > this technique to support optional acceleration modules. The pure > Python versions of pairs like profile/profile and heapq/heapq > include a try/except block at the end that does the equivalent of: > > try: > from accelerated import * # Allow accelerated overrides > except ImportError: > pass # Use pure Python versions But these identifiers will appear at the module level, not global, no? Otherwise this technique couldn't be used. I don't really understand what Tres is talking about when he writes "modules that expect to be imported this way". The imported module shouldn't care, no? This is an issue for the importing code to deal with.

Right -- "private" star imports aren't the issue for me, because the same user who creates them is responsible for the other end fo the stick. I was ranting about library authors who document star imports as the expected usage pattern for their external users.

Note that I still wouldn't use star imports in the "private acceleration" case myself. I would prefer a pattern like:

spam.py

Pure python API implementation

def foo(spat, blarg): ...

def bar(qux): ...

Replace with accelearated C implemenataion

try: import _spam except ImportError: pass # accelerated version not available else: foo = _spam.foo bar = _spam.bar

This explicit name remapping catches unintentional erros (e.g., _spam renames a method) better than the star import.

Tres. - --

Tres Seaver +1 540-429-0999 tseaver at palladion.com Palladion Software "Excellence by Design" http://palladion.com -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

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