On 11/10/2010 11:58 AM, Tres Seaver wrote:
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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.
But then you're saying that all implementations of _spam have to support
the same API. What if CPython's _spam has foo, bar, and baz, but
Jython's only has foo and bar, and IronPython's only has baz? Without
getting into special casing or lots of try/catch blocks on individual
names, I think import * is the best way to go.
Eric.
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