easy question on parsing python: "is not None"
in [Python]
|
From: Gregory Ewing on 6 Aug 2010 21:41 Steven D'Aprano wrote: > Generally, > when testing for None, you actually want None and not some look-alike > that merely tests equal to None. That's true, although I can't think of a use case for an object that compares equal to None but isn't -- except for obfuscated code competition entries and making obscure points in usenet discussions. :-) -- Greg
From: Ben Finney on 7 Aug 2010 00:28 Steven D'Aprano <steve(a)REMOVE-THIS-cybersource.com.au> writes: > On Thu, 05 Aug 2010 12:07:53 -0400, wheres pythonmonks wrote: > > > P.S. Sorry for the top-post -- is there a way to not do top posts > > from gmail? I haven't used usenet since tin. > > Er, surely you can just move the cursor before you start typing??? I like to think that the cursor is placed at the top by default so that <URL:http://en.wikipedia.org/wiki/Posting_style#Interleaved_style> is easy: just travel down through the quoted material, removing it if not relevant and inserting one's responses where needed. -- \ “Two hands working can do more than a thousand clasped in | `\ prayer.” —Anonymous | _o__) | Ben Finney
From: Stefan Schwarzer on 7 Aug 2010 03:04 Hi Steven, On 2010-08-07 00:28, Steven D'Aprano wrote: > On Fri, 06 Aug 2010 15:37:04 +0200, Stefan Schwarzer wrote: >>> Plus, I believe the >>> "==" operator will check if the variables point to the same object. >> >> No, that's what `is` is for. > > Actually, yes, equality is implemented with a short-cut that checks for > identity first. That makes something like: > [...] Oops, I didn't realize that the OP had mentioned the identity check as an optimization in case the objects are the same. I thought he was confusing the operator with `is`. > s = "abc"*1000*1000*10 > s == s > > nice and quick, as Python can immediately recognise that a string is > always equal to itself without having to walk the entire string comparing > each character with itself. Yes, that definitely makes sense. I guess I would have implemented it this way as well. :) Stefan
From: Gabriel Genellina on 7 Aug 2010 03:44 En Sat, 07 Aug 2010 04:04:06 -0300, Stefan Schwarzer <sschwarzer(a)sschwarzer.net> escribi�: > On 2010-08-07 00:28, Steven D'Aprano wrote: >> Actually, yes, equality is implemented with a short-cut that checks for >> identity first. That makes something like: >> [...] > > Oops, I didn't realize that the OP had mentioned the > identity check as an optimization in case the objects are > the same. I thought he was confusing the operator with `is`. > >> s = "abc"*1000*1000*10 >> s == s >> >> nice and quick, as Python can immediately recognise that a string is >> always equal to itself without having to walk the entire string >> comparing >> each character with itself. > > Yes, that definitely makes sense. I guess I would have > implemented it this way as well. :) For strings and other internal types this optimization certainly makes sense. For user-defined types it gets in the way and prevents defining an object such x==x is False (like NANs). -- Gabriel Genellina
From: Steven D'Aprano on 7 Aug 2010 08:05
On Sat, 07 Aug 2010 14:28:19 +1000, Ben Finney wrote: > Steven D'Aprano <steve(a)REMOVE-THIS-cybersource.com.au> writes: > >> On Thu, 05 Aug 2010 12:07:53 -0400, wheres pythonmonks wrote: >> >> > P.S. Sorry for the top-post -- is there a way to not do top posts >> > from gmail? I haven't used usenet since tin. >> >> Er, surely you can just move the cursor before you start typing??? > > I like to think that the cursor is placed at the top by default so that > <URL:http://en.wikipedia.org/wiki/Posting_style#Interleaved_style> is > easy: just travel down through the quoted material, removing it if not > relevant and inserting one's responses where needed. Yes, but apparently millions of Internet users have keyboards where neither the cursor keys nor backspace/delete works. Being unable to interleave their reply with the quoted text, they end up quoting the entire week-long thread at the bottom of every email they send. I blame Manservant Neville. -- Steven |