[Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration)
"Clayton Kirkwood" writes: > Also of confusion, the library reference says: > > Match objects always have a boolean value of True. Since match() and > search() return None when there is no match, you can test whether there was > a match with a simple if statement: > > match = re.search(pattern, string) > if match: > process(match) The documentation is incorrect, as you point out: “have a boolean value of True” implies that the value is identical to the built-in ‘True’ constant, which is never the case for these objects. Instead, the passage above should say “evaluates true in a boolean context”. Would you be so kind as to report a bug to that effect http://bugs.python.org/>? -- \ “The Vatican is not a state.… a state must have people. There | `\are no Vaticanians.… No-one gets born in the Vatican except by | _o__)an unfortunate accident.” —Geoffrey Robertson, 2010-09-18 | Ben Finney ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration)
I reported it. I feel all grown up now. Kind of like one of the boys(girls...) Clayton:<) >-Original Message- >From: Tutor [mailto:tutor-bounces+crk=godblessthe...@python.org] On >Behalf Of Ben Finney >Sent: Monday, November 10, 2014 3:24 PM >To: tutor@python.org >Subject: [Tutor] “has a value of True” versus “evaluates true” (was: >don't understand iteration) > >"Clayton Kirkwood" writes: > >> Also of confusion, the library reference says: >> >> Match objects always have a boolean value of True. Since match() and >> search() return None when there is no match, you can test whether >> there was a match with a simple if statement: >> >> match = re.search(pattern, string) >> if match: >> process(match) > >The documentation is incorrect, as you point out: “have a boolean value >of True” implies that the value is identical to the built-in ‘True’ >constant, which is never the case for these objects. > >Instead, the passage above should say “evaluates true in a boolean >context”. > >Would you be so kind as to report a bug to that effect >http://bugs.python.org/>? > >-- > \ “The Vatican is not a state.… a state must have people. There | > `\are no Vaticanians.… No-one gets born in the Vatican except by | >_o__)an unfortunate accident.” —Geoffrey Robertson, 2010-09-18 | >Ben Finney > >___ >Tutor maillist - Tutor@python.org >To unsubscribe or change subscription options: >https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration)
good catch, and definitely a distinction beginners should be more cognizant of. it's also good to recognize that a call to "bool(match)" would render that statement correct, as the built-in/factory function will return what an object evaluates to (True [re.match object] or/vs.False [None]). On Mon, Nov 10, 2014 at 5:31 PM, Clayton Kirkwood wrote: > I reported it. I feel all grown up now. Kind of like one of the > boys(girls...) > > Clayton:<) > > > >-Original Message- > >From: Tutor [mailto:tutor-bounces+crk=godblessthe...@python.org] On > >Behalf Of Ben Finney > >Sent: Monday, November 10, 2014 3:24 PM > >To: tutor@python.org > >Subject: [Tutor] “has a value of True” versus “evaluates true” (was: > >don't understand iteration) > > > >"Clayton Kirkwood" writes: > > > >> Also of confusion, the library reference says: > >> > >> Match objects always have a boolean value of True. Since match() and > >> search() return None when there is no match, you can test whether > >> there was a match with a simple if statement: > >> > >> match = re.search(pattern, string) > >> if match: > >> process(match) > > > >The documentation is incorrect, as you point out: “have a boolean value > >of True” implies that the value is identical to the built-in ‘True’ > >constant, which is never the case for these objects. > > > >Instead, the passage above should say “evaluates true in a boolean > >context”. > > > >Would you be so kind as to report a bug to that effect > >http://bugs.python.org/>? > > > >-- > > \ “The Vatican is not a state.… a state must have people. There | > > `\are no Vaticanians.… No-one gets born in the Vatican except by | > >_o__)an unfortunate accident.” —Geoffrey Robertson, 2010-09-18 | > >Ben Finney > > > >___ > >Tutor maillist - Tutor@python.org > >To unsubscribe or change subscription options: > >https://mail.python.org/mailman/listinfo/tutor > > > ___ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > https://mail.python.org/mailman/listinfo/tutor > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "A computer never does what you want... only what you tell it." +wesley chun <http://google.com/+WesleyChun> : wescpy at gmail : @wescpy <http://twitter.com/wescpy> Python training & consulting : http://CyberwebConsulting.com "Core Python" books : http://CorePython.com Python blog: http://wescpy.blogspot.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration)
So, there is a difference between None and False, is that the issue? I don’t necessarily see the difference as stated in the subject line. A=True If A == True If A Is this the crux of the issue? BTW, the feedback to my submittal suggests that this is a difference with no distinction. Clayton From: wesley chun [mailto:wes...@gmail.com] Sent: Monday, November 10, 2014 11:35 PM To: c...@godblessthe.us Cc: Ben Finney; tutor Subject: Re: [Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration) good catch, and definitely a distinction beginners should be more cognizant of. it's also good to recognize that a call to "bool(match)" would render that statement correct, as the built-in/factory function will return what an object evaluates to (True [re.match object] or/vs.False [None]). On Mon, Nov 10, 2014 at 5:31 PM, Clayton Kirkwood wrote: I reported it. I feel all grown up now. Kind of like one of the boys(girls...) Clayton:<) >-Original Message- >From: Tutor [mailto:tutor-bounces+crk <mailto:tutor-bounces%2Bcrk> >=godblessthe...@python.org] On >Behalf Of Ben Finney >Sent: Monday, November 10, 2014 3:24 PM >To: tutor@python.org >Subject: [Tutor] “has a value of True” versus “evaluates true” (was: >don't understand iteration) > >"Clayton Kirkwood" writes: > >> Also of confusion, the library reference says: >> >> Match objects always have a boolean value of True. Since match() and >> search() return None when there is no match, you can test whether >> there was a match with a simple if statement: >> >> match = re.search(pattern, string) >> if match: >> process(match) > >The documentation is incorrect, as you point out: “have a boolean value >of True” implies that the value is identical to the built-in ‘True’ >constant, which is never the case for these objects. > >Instead, the passage above should say “evaluates true in a boolean >context”. > >Would you be so kind as to report a bug to that effect >http://bugs.python.org/>? > >-- > \ “The Vatican is not a state.… a state must have people. There | > `\are no Vaticanians.… No-one gets born in the Vatican except by | >_o__)an unfortunate accident.” —Geoffrey Robertson, 2010-09-18 | >Ben Finney > >___ >Tutor maillist - Tutor@python.org >To unsubscribe or change subscription options: >https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "A computer never does what you want... only what you tell it." +wesley chun <http://google.com/+WesleyChun> : wescpy at gmail : @wescpy <http://twitter.com/wescpy> Python training & consulting : http://CyberwebConsulting.com "Core Python" books : http://CorePython.com Python blog: http://wescpy.blogspot.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] “has a value of True” versus “evaluates true” (was: don't understand iteration)
On Tue, Nov 11, 2014 at 10:24:00AM +1100, Ben Finney wrote: > "Clayton Kirkwood" writes: > > > Also of confusion, the library reference says: > > > > Match objects always have a boolean value of True. Since match() and > > search() return None when there is no match, you can test whether there was > > a match with a simple if statement: > > > > match = re.search(pattern, string) > > if match: > > process(match) > > The documentation is incorrect, as you point out: “have a boolean value > of True” implies that the value is identical to the built-in ‘True’ > constant, which is never the case for these objects. I disagree with that interpretation. "X has a boolean value of True" does not imply that X is necessarily True, but only that bool(X) is True. Is the same way we might say: Lists have a string representation with [ and ] delimiters and , item separators I trust that you wouldn't interprete that as meaning that lists *are* strings. If the documentation said that match objects *are* the boolean value True, then you would be correct, but it doesn't. Your interpretation confuses "has" for "is". To put it another way, "X has a boolean value of True" is synonymous with any of these alternative ways of saying the same thing: "X evaluates like True in a boolean context" "X is truthy" "X is a truthy value" "X is a true-like value" "X is equivalent to the bool True in boolean contexts" "X has the quality of being interpreted as true in boolean contexts" "bool(X) returns True" and many other ways of saying the same thing. > Instead, the passage above should say “evaluates true in a boolean > context”. > > Would you be so kind as to report a bug to that effect > http://bugs.python.org/>? I shouldn't bother if I were you :-) -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
