Re: why any( ) instead of firsttrue( ) ?
danieldelay danielde...@gmail.com wrote: Does GVR prefers beauty to power ? Not in the beginning, but in recent years things are tending this way. And, frankly, I don't think that's a Bad Thing at all. -- Tim Roberts, t...@probo.com Providenza Boekelheide, Inc. -- http://mail.python.org/mailman/listinfo/python-list
Re: why any( ) instead of firsttrue( ) ?
On Jun 8, 2:16 pm, danieldelay danielde...@gmail.com wrote: def firsttrue(iterable): for element in iterable: if element: return element return None This function firsttrue( ) could probably be used anywhere any( ) is used, but with the ability to retrieve the first element where bool(element) is True, which may be sometimes usefull. FWIW, it's not hard to roll your own fast itertools variants of any() and all(): next(ifilter(None, d), False) # first true, else False next(ifilterfalse(None, d), True) # first false, else True Raymond -- http://mail.python.org/mailman/listinfo/python-list
Re: why any( ) instead of firsttrue( ) ?
Le 09/06/2010 08:54, Raymond Hettinger a écrit : next(ifilter(None, d), False) Good, this is rather short and does the job !... I should try to use more often this itertools module. Thanks Daniel -- http://mail.python.org/mailman/listinfo/python-list
Re: why any( ) instead of firsttrue( ) ?
On Tue, Jun 8, 2010 at 3:16 PM, danieldelay danielde...@gmail.com wrote: This function firsttrue( ) could probably be used anywhere any( ) is used, but with the ability to retrieve the first element where bool(element) is True, which may be sometimes usefull. I suppose that there is a reason for that, does anybody know it ? Because it was designed as a replacement for reduce(lambda x, y: x or y, iterable). The problem arises when the iterable is empty. What false value should be returned? If the iterable is a sequence of bools, then None doesn't fit. If the iterable is a sequence of non-bool objects, then False doesn't fit. In the case of reduce, the problem is solved by explicitly specifying an initial value to be used when the sequence is empty, but I guess GVR didn't feel that was appropriate here. Cheers, Ian -- http://mail.python.org/mailman/listinfo/python-list
Re: why any( ) instead of firsttrue( ) ?
Le 09/06/2010 00:24, Ian Kelly a écrit :
Because it was designed as a replacement for reduce(lambda x, y: x or
y, iterable). The problem arises when the iterable is empty. What
false value should be returned? If the iterable is a sequence of
bools, then None doesn't fit. If the iterable is a sequence of
non-bool objects, then False doesn't fit. In the case of reduce, the
problem is solved by explicitly specifying an initial value to be used
when the sequence is empty, but I guess GVR didn't feel that was
appropriate here.
Cheers,
Ian
Thanks for your reply, it helps me to understand this choice wether I do
not agree with it.
False sounds natural for a function called any() which makes a
boolean calculus
None sounds natural for a function called firsttrue() which tries to
retrieve an element.
As the two make sense, I would have chosen the firsttrue() which is
more powerfull...
Perhaps any() whas choosen to keep a beautiful symmetry with all(),
that I can interprete only as a boolean calculus.
Does GVR prefers beauty to power ?
firsttrue(line.strip() for line in '\n\n \n CHEERS \n'.split('\n'))
Daniel.
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Re: why any( ) instead of firsttrue( ) ?
danieldelay wrote:
Le 09/06/2010 00:24, Ian Kelly a écrit :
Because it was designed as a replacement for reduce(lambda x, y: x or
y, iterable). The problem arises when the iterable is empty. What
false value should be returned? If the iterable is a sequence of
bools, then None doesn't fit. If the iterable is a sequence of
non-bool objects, then False doesn't fit. In the case of reduce, the
problem is solved by explicitly specifying an initial value to be used
when the sequence is empty, but I guess GVR didn't feel that was
appropriate here.
Cheers,
Ian
Thanks for your reply, it helps me to understand this choice wether I do
not agree with it.
False sounds natural for a function called any() which makes a
boolean calculus
None sounds natural for a function called firsttrue() which tries to
retrieve an element.
As the two make sense, I would have chosen the firsttrue() which is
more powerfull...
Perhaps any() whas choosen to keep a beautiful symmetry with all(),
that I can interprete only as a boolean calculus.
Does GVR prefers beauty to power ?
firsttrue(line.strip() for line in '\n\n \n CHEERS \n'.split('\n'))
Should 'firsttrue' return None? Surely, if none are true then it should
raise an exception.
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Re: why any( ) instead of firsttrue( ) ?
On 06/08/2010 06:18 PM, MRAB wrote:
danieldelay wrote:
firsttrue(line.strip() for line in '\n\n \n CHEERS \n'.split('\n'))
Should 'firsttrue' return None? Surely, if none are true then it should
raise an exception.
which can fairly elegantly be written with stock-Python as
# try:
result = itertools.ifilter(None,(
# some arbitrary generator goes here
line.strip()
for line in
'\n\n \n CHEERS \n'.split('\n')
)).next()
# except StopIteration:
#result = YOUR_DEFAULT_HERE
-tkc
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Re: why any( ) instead of firsttrue( ) ?
On Jun 8, 4:08 pm, danieldelay danielde...@gmail.com wrote:
Le 09/06/2010 00:24, Ian Kelly a crit :
Because it was designed as a replacement for reduce(lambda x, y: x or
y, iterable). The problem arises when the iterable is empty. What
false value should be returned? If the iterable is a sequence of
bools, then None doesn't fit. If the iterable is a sequence of
non-bool objects, then False doesn't fit. In the case of reduce, the
problem is solved by explicitly specifying an initial value to be used
when the sequence is empty, but I guess GVR didn't feel that was
appropriate here.
Cheers,
Ian
Thanks for your reply, it helps me to understand this choice wether I do
not agree with it.
False sounds natural for a function called any() which makes a
boolean calculus
None sounds natural for a function called firsttrue() which tries to
retrieve an element.
As the two make sense, I would have chosen the firsttrue() which is
more powerfull...
Perhaps any() whas choosen to keep a beautiful symmetry with all(),
that I can interprete only as a boolean calculus.
Does GVR prefers beauty to power ?
firsttrue(line.strip() for line in '\n\n \n CHEERS \n'.split('\n'))
Given Python's approach to boolean semantics I'm surprised they did it
that way too. Pretty much all other boolean logic in Python will
returns whatever value short circuits the operation. Based on that, I
say it'd be perfectly consistent for any() and all() to do the same.
One nitpick: if no values are true it should return the final value,
not None, because any([a,b,c]) should be exactly equivalent to a or
b or c.
My best guess why they did it that is for the interactive prompt (so
that it would print True or False). But then why didn't they do that
for and and or?
Having said that, the behavior of any() and all() is closer to the
boolean semantics I'd prefer. The current semantics tempt too many
programmers to use erroneous hacks like:
x and y or z
or merely readability-lacking hacks like:
x or y
Carl Banks
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