Re: Filter versus comprehension (was Re: something about split()???)
On Fri, Aug 24, 2012 at 3:03 PM, Walter Hurry walterhu...@lavabit.com wrote: On Fri, 24 Aug 2012 14:29:00 -0400, Dennis Lee Bieber wrote: It appears to be a change Google made in the last month or two... My hypothesis is that they are replacing hard EOL found in inbound NNTP with an HTML p, and then on outgoing replacing the p with a pair of NNTP line endings. In contrast, text composed on Google is coming in as long single lines (since quoting said text in a response produces on a at the start of the paragraph. Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? I haven't used a newsreader in over a decade. I'm quite happy with a mailing list. Am I missing something? -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On 25/08/2012 13:57, David Robinow wrote: On Fri, Aug 24, 2012 at 3:03 PM, Walter Hurry walterhu...@lavabit.com wrote: On Fri, 24 Aug 2012 14:29:00 -0400, Dennis Lee Bieber wrote: It appears to be a change Google made in the last month or two... My hypothesis is that they are replacing hard EOL found in inbound NNTP with an HTML p, and then on outgoing replacing the p with a pair of NNTP line endings. In contrast, text composed on Google is coming in as long single lines (since quoting said text in a response produces on a at the start of the paragraph. Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? I haven't used a newsreader in over a decade. I'm quite happy with a mailing list. Am I missing something? Not really. I'm the same; it just means you can skip over the occasional ggroups-newsreader discussion threads which pop up about 3 times a year on average. :) TJG -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On Wednesday, 22 August 2012 22:13:04 UTC+5:30, Terry Reedy wrote: On 8/22/2012 3:30 AM, Mark Lawrence wrote: On 22/08/2012 06:46, Terry Reedy wrote: On 8/21/2012 11:43 PM, mingqiang hu wrote: why filter is bad when use lambda ? Inefficient, not 'bad'. Because the equivalent comprehension or generator expression does not require a function call. for each item in the iterable. A case of premature optimisation? :) No, as regards my post. I simply made a factual statement without advocating a particular action. filter(lambda x: expr, iterable) (x for x in iterable if expr) both create iterators that produce the items in iterable such that bool(expr) is true. The following, with output rounded, shows something of the effect of the extra function call. timeit.timeit(list(i for i in ranger if False), ranger=range(0)) 0.91 timeit.timeit(list(i for i in ranger if False), ranger=range(20)) 1.28 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(0)) 0.83 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(20)) 2.60 Simply keeping true items is faster with filter -- at least on my particular machine with 3.3.0b2. timeit.timeit(list(filter(None, ranger)), ranger=range(20)) 1.03 Filter is also faster if the expression is a function call. timeit.timeit(list(filter(f, ranger)), ranger=range(20); f=lambda i: False) 2.5033614114454394 timeit.timeit(list(i for i in ranger if f(i)), ranger=range(20); f=lambda i: False) 3.2394095327040304 --- Perhaps or even yes as regards the so-called rule 'always use comprehension'. If one prefers filter as more readable, if one only wants to keep true items, if the expression is a function call, if evaluating the expression takes much more time than the extra function call so the latter does not matter, if the number of items is few enough that the extra time does not matter, then the rule is not needed or even wrong. So I think PyLint should be changed to stop its filter fud. -- Terry Jan Reedy When filtering for true values, filter(None,xxx) can be used Your examples with lambda i:False are unrealistic - you are comparing `if False` vs lambda function(xx) - function call vs boolean check -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On 8/24/2012 10:44 AM, Ramchandra Apte wrote: On Wednesday, 22 August 2012 22:13:04 UTC+5:30, Terry Reedy wrote: timeit.timeit(list(i for i in ranger if False), ranger=range(0)) 0.91 timeit.timeit(list(i for i in ranger if False), ranger=range(20)) 1.28 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(0)) 0.83 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(20)) 2.60 Your mail agent in inserting blank lines in quotes -- google? See if you can turn that off. Your examples with lambda i:False are unrealistic - you are comparing `if False` vs lambda function(xx) - function call vs boolean check That is exactly the comparison I wanted to make. The iteration + boolean check takes .37 for 20 items, the iteration + call 1.77. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On Fri, 24 Aug 2012 14:29:00 -0400, Dennis Lee Bieber wrote: It appears to be a change Google made in the last month or two... My hypothesis is that they are replacing hard EOL found in inbound NNTP with an HTML p, and then on outgoing replacing the p with a pair of NNTP line endings. In contrast, text composed on Google is coming in as long single lines (since quoting said text in a response produces on a at the start of the paragraph. Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On 8/24/2012 5:56 PM, Dennis Lee Bieber wrote: On Fri, 24 Aug 2012 19:03:51 + (UTC), Walter Hurry walterhu...@lavabit.com declaimed the following in gmane.comp.python.general: Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? Probably because their ISP doesn't offer a free server G Python lists are available on the free gmane mail-to-news server. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On 8/24/2012 3:03 PM Terry Reedy said... On 8/24/2012 5:56 PM, Dennis Lee Bieber wrote: On Fri, 24 Aug 2012 19:03:51 + (UTC), Walter Hurry walterhu...@lavabit.com declaimed the following in gmane.comp.python.general: Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? Probably because their ISP doesn't offer a free server G Python lists are available on the free gmane mail-to-news server. I'm getting high load related denials with the gmane connections a lot recently so I'm open to alternatives. Suggestions or recommendations? Emile -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On 24/08/2012 23:03, Terry Reedy wrote: On 8/24/2012 5:56 PM, Dennis Lee Bieber wrote: On Fri, 24 Aug 2012 19:03:51 + (UTC), Walter Hurry walterhu...@lavabit.com declaimed the following in gmane.comp.python.general: Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? Probably because their ISP doesn't offer a free server G Python lists are available on the free gmane mail-to-news server. I don't think the core-mentorship list is available on gmane. Have I missed it, has nobody asked for it to go on there or what? -- Cheers. Mark Lawrence. -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
In article k18uat$9ns$1...@ger.gmane.org, Emile van Sebille em...@fenx.com wrote: On 8/24/2012 3:03 PM Terry Reedy said... Python lists are available on the free gmane mail-to-news server. I'm getting high load related denials with the gmane connections a lot recently so I'm open to alternatives. The high load denials should be a thing of the past as the gmane NNTP server was very recently upgraded to use SSDs instead of standard disks. -- Ned Deily, n...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
In article k18v53$hgs$1...@ger.gmane.org, Mark Lawrence breamore...@yahoo.co.uk wrote: I don't think the core-mentorship list is available on gmane. Have I missed it, has nobody asked for it to go on there or what? core-mentorship is a closed list so it would not be appropriate for it to be mirrored anywhere. http://mail.python.org/mailman/listinfo/core-mentorship -- Ned Deily, n...@acm.org -- http://mail.python.org/mailman/listinfo/python-list
Re: Filter versus comprehension (was Re: something about split()???)
On Fri, 24 Aug 2012 17:56:47 -0400, Dennis Lee Bieber wrote: On Fri, 24 Aug 2012 19:03:51 + (UTC), Walter Hurry walterhu...@lavabit.com declaimed the following in gmane.comp.python.general: Google Groups sucks. These are computer literate people here. Why don't they just use a proper newsreader? Probably because their ISP doesn't offer a free server G There are plenty of free Usenet providers. -- http://mail.python.org/mailman/listinfo/python-list
Filter versus comprehension (was Re: something about split()???)
On 8/22/2012 3:30 AM, Mark Lawrence wrote: On 22/08/2012 06:46, Terry Reedy wrote: On 8/21/2012 11:43 PM, mingqiang hu wrote: why filter is bad when use lambda ? Inefficient, not 'bad'. Because the equivalent comprehension or generator expression does not require a function call. for each item in the iterable. A case of premature optimisation? :) No, as regards my post. I simply made a factual statement without advocating a particular action. filter(lambda x: expr, iterable) (x for x in iterable if expr) both create iterators that produce the items in iterable such that bool(expr) is true. The following, with output rounded, shows something of the effect of the extra function call. timeit.timeit(list(i for i in ranger if False), ranger=range(0)) 0.91 timeit.timeit(list(i for i in ranger if False), ranger=range(20)) 1.28 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(0)) 0.83 timeit.timeit(list(filter(lambda i: False, ranger)), ranger=range(20)) 2.60 Simply keeping true items is faster with filter -- at least on my particular machine with 3.3.0b2. timeit.timeit(list(filter(None, ranger)), ranger=range(20)) 1.03 Filter is also faster if the expression is a function call. timeit.timeit(list(filter(f, ranger)), ranger=range(20); f=lambda i: False) 2.5033614114454394 timeit.timeit(list(i for i in ranger if f(i)), ranger=range(20); f=lambda i: False) 3.2394095327040304 --- Perhaps or even yes as regards the so-called rule 'always use comprehension'. If one prefers filter as more readable, if one only wants to keep true items, if the expression is a function call, if evaluating the expression takes much more time than the extra function call so the latter does not matter, if the number of items is few enough that the extra time does not matter, then the rule is not needed or even wrong. So I think PyLint should be changed to stop its filter fud. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
