<div class="gmail_quote">On Sun, Apr 22, 2012 at 1:26 AM, Nick Coghlan <span dir="ltr"><<a href="mailto:ncoghlan@gmail.com">ncoghlan@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im">On Sun, Apr 22, 2012 at 11:06 AM, Eric V. Smith <<a href="mailto:eric@trueblade.com">eric@trueblade.com</a>> wrote:<br>
> Furthermore, given how __path__ is built, by one-at-a-time remembering<br>
> the path entries that have a foo directory but no foo/__init__.py, I'm<br>
> not sure how you'd turn that into some auto-updating iterable.<br>
<br>
</div>You just have to remember all your namespace packages somewhere and<br>
then use a list subclass that triggers a rescan whenever the contents<br>
change.<br></blockquote><div><br></div><div>Not necessary if you set __path__ to an iterable that caches a tuple of its parent package __path__ (or sys.path), and compares that against the current value before iterating. If it's changed, you walk the parent and rescan, otherwise iterate over your cached value. I posted a sketch to Python-Dev the first time 402 discussion happened there.</div>
<div><br></div><div>The consequences of making namespace package __path__ iterable are less problematic, I believe, than changing the type of sys.path: almost no code manipulates __path__ as anything but an iterable, and code that does is broken for namespace packages anyway, because accessing specific offsets won't give you what you think you're looking for. So you get noisy breakage instead of quiet breakage in such cases (as would happen with using lists for __path__).</div>
<div><br></div><div>If for some reason you want to explicitly change a namespace package's __path__, you could just reset __path__ to list(__path__), and proceed from there -- which is the recommended idiom for using extend_path, anyway.</div>
<div> </div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Personally, I'm happier with the basic behaviour being that<br>
dynamically updating sys.path while the program is running can be a<br>
bit hit-or-miss in terms of what recognises the change.<br></blockquote><div><br></div><div>pkg_resources supports dynamic updating today, so the idea here was to make it possible to do away with that. (It only supports updating if it's the one doing the sys.path manipulation, however.)</div>
<div><br></div><div>I think there should be *some* blessed API(s) to force the updating, though, even if it's not automatic or dynamic. extend_path() really isn't the right tool for the job.</div><div><br></div><div>
The main argument in favor of automatic updating is that it more closely matches naive expectations of users coming from other languages. (Although to be honest I'm not 100% certain that those other languages actually do change their lookups that dynamically.)</div>
<div><br></div><div>Anyway, the sketch (using PEP 402's importer protocol; not updated for 420) was something like:</div><div><br></div><div><div><font face="'courier new', monospace">class VirtualPath:</font></div>
<div><font face="'courier new', monospace"> __slots__ = ('__name__', '_parent', '_last_seen', '_path')</font></div><div><font face="'courier new', monospace"><br></font></div>
<div><font face="'courier new', monospace"> def __init__(self, name, parent_path):</font></div><div><font face="'courier new', monospace"> self.__name__ = name</font></div><div><font face="'courier new', monospace"> self._parent = parent_path</font></div>
<div><font face="'courier new', monospace"> self._path = self._last_seen = ()</font></div><div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def _fail(self, *args, **kw):</font></div>
<div><font face="'courier new', monospace"> raise TypeError(self.__name__+" is a virtual package")</font></div><div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> __getitem__ = __setitem__ = __delitem__ = append = extend = insert = _fail</font></div>
<div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def _calculate(self):</font></div><div><font face="'courier new', monospace"> with _ImportLockContext():</font></div>
<div><font face="'courier new', monospace"> parent = tuple(self._parent)</font></div><div><font face="'courier new', monospace"> if parent != self._last_seen:</font></div><div><font face="'courier new', monospace"> items = []</font></div>
<div><font face="'courier new', monospace"> name = self.__name__</font></div><div><font face="'courier new', monospace"> for entry in parent:</font></div><div><font face="'courier new', monospace"> importer = get_importer(entry)</font></div>
<div><font face="'courier new', monospace"> if hasattr(importer, 'get_subpath'):</font></div><div><font face="'courier new', monospace"> item = importer.get_subpath(name)</font></div>
<div><font face="'courier new', monospace"> if item is not None:</font></div><div><font face="'courier new', monospace"> items.append(item)</font></div><div>
<font face="'courier new', monospace"> self._last_seen = parent</font></div><div><font face="'courier new', monospace"> self._path = tuple(items)</font></div><div><font face="'courier new', monospace"> return self._path</font></div>
<div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def __iter__(self):</font></div><div><font face="'courier new', monospace"> return iter(self._calculate())</font></div>
<div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def __len__(self):</font></div><div><font face="'courier new', monospace"> return len(self._calculate())</font></div>
<div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def __repr__(self):</font></div><div><font face="'courier new', monospace"> return "VirtualPath" + repr((self.__name__, self._parent))</font></div>
<div><font face="'courier new', monospace"><br></font></div><div><font face="'courier new', monospace"> def __contains__(self, item):</font></div><div><font face="'courier new', monospace"> return item in self._calculate()</font></div>
</div><div><br></div><div><br></div><div>Using these objects in place of lists for __path__ objects would then do the trick.</div><div><br></div><div>(And of course, you'd want to change "Virtual" to "Namespace" throughout, I suppose. ;-) )</div>
<div><br></div></div>