Thank you Jeff for the clarification. Thought so that could be something like this, but was not so clear on spot.
Tuesday, August 14, 2007, 4:15:48 PM, you wrote: JS> On 8/14/07, Adam Groszer <[EMAIL PROTECTED]> wrote: >> A strange thing happened today: >> >>> x = LocationProxy(None, "foo", "bar") >> >>> x is None >> False >> >>> x == None >> True >> >> Is this OK or I'm just missing something? JS> You have to understand how Python's ``is`` differs from ``==``. An JS> `is` check is an identity check, not an equality check. It's generally JS> faster than comparing equality. It's basically like this:: JS> a is b if id(a) == id(b) JS> The Python `id` function is basically a memory address of that JS> specific instance. None, True, and False are all basically constants JS> that have the same identity unless that name is overridden in a local JS> namespace. JS> When proxies enter the picture, you're wrapping the object with a JS> proxy, so it's no longer the same by identity. JS> >>> from zope.location import LocationProxy JS> >>> located_none = LocationProxy(None, "foo", "bar") JS> >>> id(None) JS> 3120456 JS> >>> id(located_none) JS> 404616 JS> >>> id(None) == id(located_none) JS> False JS> >>> located_none is None JS> False JS> Since the proxy object is masquerading as its wrapped object, equality JS> checks works. But identity doesn't. The `zope.proxy` package includes JS> some functions that you can use for help. JS> >>> from zope.proxy import removeAllProxies, sameProxiedObjects, isProxy JS> >>> isProxy(None) JS> False JS> >>> isProxy(located_none) JS> True JS> You have the option of removing all proxies, which would return the JS> object wrapped up by the proxy. Since we wrapped up None, it would JS> return the actual None object and identity checks would pass: JS> >>> removeAllProxies(located_none) is None JS> True JS> Or you can use `sameProxiedObjects`, which does the identity check on JS> the internal objects of one or two proxies: JS> >>> sameProxiedObjects(located_none, None) JS> True JS> You can see this when wrapping another instance of None with a location proxy. JS> >>> singing_nun = LocationProxy(None, 'austria', 'jane') JS> >>> id(singing_nun) JS> 7378424 JS> >>> singing_nun is located_none JS> False JS> >>> sameProxiedObjects(singing_nun, located_none) JS> True -- Best regards, Groszer Adam -- Quote of the day: Doubters invert the metaphor and insist that they need faith as big as a mountain in order to move a mustard seed. - Anonymous _______________________________________________ Zope3-dev mailing list Zope3-dev@zope.org Unsub: http://mail.zope.org/mailman/options/zope3-dev/archive%40mail-archive.com
