conditional expression sought

[Elaine Jackson]

If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j without
evaluating any other B_i. This is such a useful mode of expression that I would
like to be able to use something similar even when there is an i with
bool(B_i)==Fals e. The only thing I can think of by myself is ( (A_1 and [B_1])
or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for obvious
reasons. Does anybody know a good way to express this? Any help will be mucho
appreciado.

Peace

[Sidharth Kuruvila]

Re: conditional expression sought

since True and False
can also evaluate as 1 and 0
you can use the binary operators
| and &
for or and and respectively
[color=blue][color=green][color=darkred]
>>> class F:[/color][/color][/color]
.... a = 5
.... def b(self):
.... self.a = 4
.... return True
.... def a(self):
.... self.a = 1
.... return False
....[color=blue][color=green][color=darkred]
>>> g = F()
>>> g.a() & g.b()[/color][/color][/color]
False[color=blue][color=green][color=darkred]
>>> g.a[/color][/color][/color]
4
"Elaine Jackson" <elainejackson7 355@home.com> wrote in message
news:pRbSb.3303 34$ts4.37644@pd 7tw3no...[color=blue]
> If bool(B_i)==True for 1<=i<=n and j is the smallest i with[/color]
bool(A_j)==True ,[color=blue]
> then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j[/color]
without[color=blue]
> evaluating any other B_i. This is such a useful mode of expression that I[/color]
would[color=blue]
> like to be able to use something similar even when there is an i with
> bool(B_i)==Fals e. The only thing I can think of by myself is ( (A_1 and[/color]
[B_1])[color=blue]
> or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for[/color]
obvious[color=blue]
> reasons. Does anybody know a good way to express this? Any help will be[/color]
mucho[color=blue]
> appreciado.
>
> Peace
>
>[/color]

[Mark McEahern]

Re: conditional expression sought

Elaine Jackson wrote:
[color=blue]
>If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
>then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j without
>evaluating any other B_i. This is such a useful mode of expression that I would
>like to be able to use something similar even when there is an i with
>bool(B_i)==Fal se. The only thing I can think of by myself is ( (A_1 and [B_1])
>or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for obvious
>reasons. Does anybody know a good way to express this? Any help will be mucho
>appreciado.
>[/color]
Why not write a unit test that demonstrates the behavior you want?
It'll then likely be obvious to someone both what your problem is and
what a likely solution is.

Cheers,

// m

[wes weston]

ditto

Preferably, a program that runs or a screen dump.

Mark McEahern wrote:[color=blue]
> Elaine Jackson wrote:
>[color=green]
>> If bool(B_i)==True for 1<=i<=n and j is the smallest i with
>> bool(A_j)==True ,
>> then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns
>> B_j without
>> evaluating any other B_i. This is such a useful mode of expression
>> that I would
>> like to be able to use something similar even when there is an i with
>> bool(B_i)==Fals e. The only thing I can think of by myself is ( (A_1
>> and [B_1])
>> or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for
>> obvious
>> reasons. Does anybody know a good way to express this? Any help will
>> be mucho
>> appreciado.
>>[/color]
> Why not write a unit test that demonstrates the behavior you want?
> It'll then likely be obvious to someone both what your problem is and
> what a likely solution is.
>
> Cheers,
>
> // m
>[/color]

[Corey Coughlin]

Re: conditional expression sought

"Elaine Jackson" <elainejackson7 355@home.com> wrote in message news:<pRbSb.330 334$ts4.37644@p d7tw3no>...[color=blue]
> If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
> then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j without
> evaluating any other B_i. This is such a useful mode of expression that I would
> like to be able to use something similar even when there is an i with
> bool(B_i)==Fals e. The only thing I can think of by myself is ( (A_1 and [B_1])
> or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for obvious
> reasons. Does anybody know a good way to express this? Any help will be mucho
> appreciado.
>
> Peace[/color]

Oh, this must be part of your truth table script. Interesting,
looking for something like a fast SOP evaluator, or more like a
function evaluation mechanism? It would probably be most useful to
share your containers for A and B. Are you really going to have
variables named A_1 to A_n, or will you just have a vector A[0:n]?
The vector would probably be easier to deal with. Using integer
representations for your boolean vectors is a good idea, and will
probably buy you enough speed that you won't need a more serious form
of short circuit evaluation, I imagine. Unless your vectors are very
large indeed. Hmm...

[Dave K]

Re: conditional expression sought

On Thu, 29 Jan 2004 17:58:45 GMT in comp.lang.pytho n, "Elaine Jackson"
<elainejackson7 355@home.com> wrote:
[color=blue]
>If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
>then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j without
>evaluating any other B_i. This is such a useful mode of expression that I would
>like to be able to use something similar even when there is an i with
>bool(B_i)==Fal se. The only thing I can think of by myself is ( (A_1 and [B_1])
>or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for obvious
>reasons. Does anybody know a good way to express this? Any help will be mucho
>appreciado.
>
>Peace
>[/color]

I'm not sure if this is what you're looking for, but for i > a very
small number, the zip function seems more appropriate:
[color=blue][color=green][color=darkred]
>>> def get_B_i(A, B):[/color][/color][/color]
for a, b in zip(A, B):
if a: return b
return A[-1][color=blue][color=green][color=darkred]
>>> print get_B_i([False, False, True, False], [0, 1, 2, 3])[/color][/color][/color]
2[color=blue][color=green][color=darkred]
>>> print get_B_i([False, False, False, False], [0, 1, 2, 3])[/color][/color][/color]
False

This has exactly the same effect provided that A and B are the same
length, otherwise the return value by failure should be adjusted to
whatever suits your purpose.

If you really want to write a conditional expression out in full, I
can't think of anything non-clumsy that would work for all possible
values of B_i, so unfortunately can't help you there.

Dave

[Elaine Jackson]

Re: conditional expression sought

Sorry to take so long but I wasn't sure what a "unit test" was (the other guy's
post clarified it). Tell me if this isn't what you're looking for:

falsies=[0,0.0,[],(),{},'',None]
truies=[49,3.14,[1,2,3],(4,5,6),{7:8,9 :10},'nonempty']

def demo(A,B):
print "If A is ",A
print "and B is ",B
print "then (A[0] and B[0]) or (A[1] and B[1]) or (A[2] and B[2]) = ",
print (A[0] and B[0]) or (A[1] and B[1]) or (A[2] and B[2])

A=[]
from random import randint
for i in range(3):
A.append(bool(r andint(0,1)))
B=truies[0:3]
demo(A,B)

A=[False,False,Fal se]
B=falsies[0:3]
demo(A,B)
print "I would have liked this to be B[2] = ",B[2]


"Mark McEahern" <mark@mceahern. com> wrote in message
news:mailman.10 00.1075402284.1 2720.python-list@python.org ...
| Elaine Jackson wrote:
|
| >If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
| >then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j
without
| >evaluating any other B_i. This is such a useful mode of expression that I
would
| >like to be able to use something similar even when there is an i with
| >bool(B_i)==Fal se. The only thing I can think of by myself is ( (A_1 and
[B_1])
| >or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for
obvious
| >reasons. Does anybody know a good way to express this? Any help will be mucho
| >appreciado.
| >
| Why not write a unit test that demonstrates the behavior you want?
| It'll then likely be obvious to someone both what your problem is and
| what a likely solution is.
|
| Cheers,
|
| // m
|

[wes weston]

Re: conditional expression sought

Elaine,
The last code line:

print "I would have liked this to be B[2] = ",B[2]

prints the value of B[2]; the value you don't want.
I think what you meant was that you want B[2] to be
0.0 not false. bool(0.0) does equal false.
---------------------------------------------------
The code:

A.append(bool(r andint(0,1)))

will always yield an A of [true,true,true]
---------------------------------------------------
I didn't know this about python, and I'm not sure I
like it:

wes@linux:~/amy> python
[color=blue][color=green][color=darkred]
>>> print 1.1 and 2.2[/color][/color][/color]
2.2[color=blue][color=green][color=darkred]
>>> print 2.2 and 1.1[/color][/color][/color]
1.1[color=blue][color=green][color=darkred]
>>> print (1.1 and 2.2)[/color][/color][/color]
2.2

The order is important. To me, it should be printing true
and not either number or the last number.

[Elaine Jackson]

Re: conditional expression sought

This is a good idea. Thanks for pointing it out.

"Dave K" <dk123456789@RE MOVEhotmail.com > wrote in message
news:866j101bbu uhtpan29eop9o4m k1mt7nckn@4ax.c om...
| On Thu, 29 Jan 2004 17:58:45 GMT in comp.lang.pytho n, "Elaine Jackson"
| <elainejackson7 355@home.com> wrote:
|
| >If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
| >then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j
without
| >evaluating any other B_i. This is such a useful mode of expression that I
would
| >like to be able to use something similar even when there is an i with
| >bool(B_i)==Fal se. The only thing I can think of by myself is ( (A_1 and
[B_1])
| >or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for
obvious
| >reasons. Does anybody know a good way to express this? Any help will be mucho
| >appreciado.
| >
| >Peace
| >
|
| I'm not sure if this is what you're looking for, but for i > a very
| small number, the zip function seems more appropriate:
|
| >>> def get_B_i(A, B):
| for a, b in zip(A, B):
| if a: return b
| return A[-1]
| >>> print get_B_i([False, False, True, False], [0, 1, 2, 3])
| 2
| >>> print get_B_i([False, False, False, False], [0, 1, 2, 3])
| False
|
| This has exactly the same effect provided that A and B are the same
| length, otherwise the return value by failure should be adjusted to
| whatever suits your purpose.
|
| If you really want to write a conditional expression out in full, I
| can't think of anything non-clumsy that would work for all possible
| values of B_i, so unfortunately can't help you there.
|
| Dave
|
|

[Elaine Jackson]

Re: conditional expression sought

This is just for theoretical interest. The A_i's and B_i's were meant as
metavariables.

"Corey Coughlin" <corey.coughlin @attbi.com> wrote in message
news:a8623416.0 401291625.594a9 768@posting.goo gle.com...
| "Elaine Jackson" <elainejackson7 355@home.com> wrote in message
news:<pRbSb.330 334$ts4.37644@p d7tw3no>...
| > If bool(B_i)==True for 1<=i<=n and j is the smallest i with bool(A_j)==True ,
| > then the evaluation of (A_1 and B_1) or ... or (A_n and B_n) returns B_j
without
| > evaluating any other B_i. This is such a useful mode of expression that I
would
| > like to be able to use something similar even when there is an i with
| > bool(B_i)==Fals e. The only thing I can think of by myself is ( (A_1 and
[B_1])
| > or ... or (A_n and [B_n]) )[0], and I can't be satisfied with that for
obvious
| > reasons. Does anybody know a good way to express this? Any help will be
mucho
| > appreciado.
| >
| > Peace
|
| Oh, this must be part of your truth table script. Interesting,
| looking for something like a fast SOP evaluator, or more like a
| function evaluation mechanism? It would probably be most useful to
| share your containers for A and B. Are you really going to have
| variables named A_1 to A_n, or will you just have a vector A[0:n]?
| The vector would probably be easier to deal with. Using integer
| representations for your boolean vectors is a good idea, and will
| probably buy you enough speed that you won't need a more serious form
| of short circuit evaluation, I imagine. Unless your vectors are very
| large indeed. Hmm...

[Elaine Jackson]

Re: conditional expression sought

Thanks for your help. I just looked at some values of random.randint( 0,1) in my
interpreter, and one of them was 0. Getting nonboolean values from conjunction
and disjunction allows conditional evaluation of expressions; for example:
reciprocal = lambda x: (x!=0 and 1.0/x) or (x==0 and "undefined" ).

"wes weston" <wweston@att.ne t> wrote in message
news:6PjSb.1384 87$6y6.2697536@ bgtnsc05-news.ops.worldn et.att.net...
| Elaine,
| The last code line:
|
| print "I would have liked this to be B[2] = ",B[2]
|
| prints the value of B[2]; the value you don't want.
| I think what you meant was that you want B[2] to be
| 0.0 not false. bool(0.0) does equal false.
| ---------------------------------------------------
| The code:
|
| A.append(bool(r andint(0,1)))
|
| will always yield an A of [true,true,true]
| ---------------------------------------------------
| I didn't know this about python, and I'm not sure I
| like it:
|
| wes@linux:~/amy> python
|
| >>> print 1.1 and 2.2
| 2.2
| >>> print 2.2 and 1.1
| 1.1
| >>> print (1.1 and 2.2)
| 2.2
|
| The order is important. To me, it should be printing true
| and not either number or the last number.
|

[wes weston]

Re: conditional expression sought

oops;

The code:

A.append(bool(r andint(0,1)))

will always yield an A of [true,true,true]


WRONG; was thinking it was a rand float;.


Thanks for replying to all who tried to help.

wes



wes weston wrote:[color=blue]
> Elaine,
> The last code line:
>
> print "I would have liked this to be B[2] = ",B[2]
>
> prints the value of B[2]; the value you don't want.
> I think what you meant was that you want B[2] to be
> 0.0 not false. bool(0.0) does equal false.
> ---------------------------------------------------
> The code:
>
> A.append(bool(r andint(0,1)))
>
> will always yield an A of [true,true,true]
> ---------------------------------------------------
> I didn't know this about python, and I'm not sure I
> like it:
>
> wes@linux:~/amy> python
>[color=green][color=darkred]
> >>> print 1.1 and 2.2[/color][/color]
> 2.2[color=green][color=darkred]
> >>> print 2.2 and 1.1[/color][/color]
> 1.1[color=green][color=darkred]
> >>> print (1.1 and 2.2)[/color][/color]
> 2.2
>
> The order is important. To me, it should be printing true
> and not either number or the last number.
>[/color]