[Tutor] Vol 127, Issue 15
Crush
crushed26 at gmail.com
Fri Sep 5 23:32:34 CEST 2014
Ok nevermind, I did not figure it out. My code...
count = 0
while count < 3:
count += 1
Subprocess.Popen('command')
if count == 3:
sys.exit()
This does not work as I want it to; it consecutively executes the command three times in a row. I only want it to execute once. However, if there is an error, I want it to try again, but only if count does not equal 3. If count equals 3, i want it to give up and exit or do something else.
Bo
> On Sep 5, 2014, at 4:40 PM, tutor-request at python.org wrote:
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> Today's Topics:
>
> 1. Re: How to count vehicle? I'm trying but my code don't
> increasing.. (Whees Northbee)
> 2. Re: How to count vehicle? I'm trying but my code don't
> increasing.. (Steven D'Aprano)
> 3. Re: How to count vehicle? I'm trying but my code don't
> increasing.. (Marc Tompkins)
> 4. How to detect colinearity? (Danny Yoo)
> 5. command counter (Bo Morris)
> 6. command counter (Bo Morris)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 5 Sep 2014 18:09:45 +0700
> From: Whees Northbee <ch.de2.2309 at gmail.com>
> To: Danny Yoo <dyoo at hashcollision.org>
> Cc: "tutor at python.org" <tutor at python.org>
> Subject: Re: [Tutor] How to count vehicle? I'm trying but my code
> don't increasing..
> Message-ID:
> <CAGPegViH=pGbcQ-n1Wukwy0e1b=S=twje=L01ccGMjA0yr64zA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I'm really sorry if my post doesn't appropriate to the forum rule.. I
> already asked in other forums 2 months ago, but no answer or had voted down
> and closed.. If you ask me about the basic slope formula or basic theory of
> intersection of point with a line I know, that's why I try with "if" code
> since the line is have the same y coordinate there's no slope, so I think
> if the y coordinate point same with y coordinate line no matter the value
> of x coordinate as long as the y coordinate same, the counter increasing..
> but if you're think I'm expert with python because I'm work with computer
> vision I'm not I'm newbie to both.. I'm sorry..
>
>
> On Wed, Sep 3, 2014 at 6:04 AM, Danny Yoo <dyoo at hashcollision.org> wrote:
>
>>>
>>> On Tue, Sep 2, 2014 at 7:01 AM, Whees Northbee <ch.de2.2309 at gmail.com>
>> wrote:
>>>> If all of these confusing, I'll simplify the problem, I need to know if
>> a
>>>> point (x,y) exactly at a line where line is (ax1,ay) to (ax2,ay)..
>>>
>>>
>>> Case in point: in the question above, you can't possibly be asking us
>>> to help you write a predicate that tells whether a point is on a line.
>>> So I have to be misunderstanding your question. You must be asking
>>> for a library function in OpenCV, and I'm pretty sure none of us are
>>> OpenCV experts.
>>
>>
>> Ok, found an OpenCV-specific answer about this:
>>
>>
>> http://stackoverflow.com/questions/5596805/opencv-detect-if-points-lie-along-line-plane
>>
>> As expected, this is very domain-specific, and probably not suitable
>> for Python-tutor.
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> ------------------------------
>
> Message: 2
> Date: Sat, 6 Sep 2014 03:40:43 +1000
> From: Steven D'Aprano <steve at pearwood.info>
> To: tutor at python.org
> Subject: Re: [Tutor] How to count vehicle? I'm trying but my code
> don't increasing..
> Message-ID: <20140905174043.GQ9293 at ando.pearwood.info>
> Content-Type: text/plain; charset=us-ascii
>
>> On Fri, Sep 05, 2014 at 06:09:45PM +0700, Whees Northbee wrote:
>> I'm really sorry if my post doesn't appropriate to the forum rule.. I
>> already asked in other forums 2 months ago, but no answer or had voted down
>> and closed..
>
> It's not a matter about breaking some rule, but about you getting an
> answer. Your question is very narrowly specific to a particular software
> library. Of all the people here, YOU probably know more about it than
> all the rest of us together.
>
> Even though OpenCV *uses* Python, your question is not about Python. It
> is about computer vision, and we know less than you about computer
> vision.
>
>
>
> --
> Steven
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 5 Sep 2014 10:41:03 -0700
> From: Marc Tompkins <marc.tompkins at gmail.com>
> To: Whees Northbee <ch.de2.2309 at gmail.com>
> Cc: "tutor at python.org" <tutor at python.org>
> Subject: Re: [Tutor] How to count vehicle? I'm trying but my code
> don't increasing..
> Message-ID:
> <CAKK8jXboTmu6hyTRuPimw2Mr4J0uO+v+wkzUeL2TTr3pu6dX+g at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
>> On Fri, Sep 5, 2014 at 4:09 AM, Whees Northbee <ch.de2.2309 at gmail.com> wrote:
>> I'm really sorry if my post doesn't appropriate to the forum rule.. I
>> already asked in other forums 2 months ago, but no answer or had voted down
>> and closed..
>
> It's not that you've broken a rule. It's just that you're asking on a
> forum where you're not likely to get an answer, because nobody here
> (that I am aware of) is an expert in computer vision. The way you
> phrased the question at first made it sound like you were asking about
> the basic math - we can help you with that, and with turning that math
> into Python. But for questions about OpenCV, you're going to have to
> ask in a place where people actually use OpenCV. It's not a matter of
> etiquette or forum rules - it's a matter of asking in a place where
> people can actually answer your question. If you asked in OpenCV
> forums, and got no answer/voted down... we're sorry, but we can't
> really help you with that.
>
>
> ------------------------------
>
> Message: 4
> Date: Fri, 5 Sep 2014 12:35:17 -0700
> From: Danny Yoo <dyoo at hashcollision.org>
> To: Whees Northbee <ch.de2.2309 at gmail.com>
> Cc: "tutor at python.org" <tutor at python.org>
> Subject: [Tutor] How to detect colinearity?
> Message-ID:
> <CAGZAPF5fY27nAJmFLBn_N6KM0j4LFpn1QzigPWCzOfgKzgh2hw at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
>> But if you're think I'm expert with python because I'm work with computer vision
>> I'm not I'm newbie to both..
>
> Ok. Since you've stated that you are a beginner, we now have to
> recalibrate how we're answering your questions.
>
> In that case, I would strongly suggest going through a basic
> programming tutorial first, before tackling anything with computer
> vision. Otherwise, you'll keep getting tripped up on issues that
> people will assume you already know about.
>
> There are several tutorials you can take a look at:
>
> https://wiki.python.org/moin/BeginnersGuide/NonProgrammers
>
> Personally, I like:
>
> http://openbookproject.net/thinkcs/python/english2e/
>
> but the other tutorials from the link above should be fine.
>
>
>
>> If you ask me about the basic slope formula or basic theory of
>> intersection of point with a line I know, that's why I try with "if" code
>> since the line is have the same y coordinate there's no slope, so I think if
>> the y coordinate point same with y coordinate line no matter the value of x
>> coordinate as long as the y coordinate same, the counter increasing.
>
> So you've tried to use the idea of slope, but have discovered that
> when the line is vertical, using a slope approach does not work on
> such lines. Yes. That's one of the problems with using the slope
> approach.
>
> There are more general approaches that avoid the whole slope problem, such as:
>
> http://stackoverflow.com/questions/328107/how-can-you-determine-a-point-is-between-two-other-points-on-a-line-segment
>
> which talks about an alternative approach. The proposed function they
> use there is:
>
> #############################################################
> def isBetween(a, b, c):
> crossproduct = (c.y - a.y) * (b.x - a.x) - (c.x - a.x) * (b.y - a.y)
> if abs(crossproduct) > epsilon : return False
>
> dotproduct = (c.x - a.x) * (b.x - a.x) + (c.y - a.y) * (b.y - a.y)
> if dotproduct < 0 : return False
>
> squaredlengthba = (b.x - a.x) * (b.x - a.x) + (b.y - a.y) * (b.y - a.y)
> if dotproduct > squaredlengthba: return False
>
> return True
> #############################################################
>
> where a, b, and c are objects with x and y components. It's more
> general because it doesn't use division: rather, they use cross
> products and dot products. Vector arithmetic to the rescue,
> basically.
>
>
> But note the "epsilon" free variable there: that's an indication that
> we have to be careful about floating point arithmetic.
>
> I used the term "floating point arithmetic" earlier in one of my first
> replies because I hoped that would trigger concepts that I had assumed
> that you had learned about already.
>
> I saw that you were using exact equality on numbers, and for folks who
> have done some beginner-style computer arithmetic, the term "floating
> point arithmetic" should be a big warning sign to be careful about
> equality.
>
> But now that you've said more of your background, I can't assume you
> know what "floating point" arithmetic means.
>
> Please read:
>
> https://docs.python.org/2/tutorial/floatingpoint.html
>
> for a brief introduction.
>
> After reading that, you should have a better understanding as to why
> your programs not use exact equality when floating point numbers are
> concerned.
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 5 Sep 2014 16:32:17 -0400
> From: Bo Morris <crushed26 at gmail.com>
> To: "tutor at python.org" <tutor at python.org>
> Subject: [Tutor] command counter
> Message-ID:
> <CAKKCnfdz1x=RuU9pKR=HrPRUhAGs6f5w97Ge33sYwp3r59ZgLw at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> how would I keep track of count for each time a command exectuted? for
> example...
>
> subprocess.Popen("command") && add 1 to count. If count equals n number, do
> something.
>
> I have tried count = 0 count += 1, but count does not seem to be
> incrementing.
>
> Thanks
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> ------------------------------
>
> Message: 6
> Date: Fri, 5 Sep 2014 16:40:08 -0400
> From: Bo Morris <crushed26 at gmail.com>
> To: "tutor at python.org" <tutor at python.org>
> Subject: [Tutor] command counter
> Message-ID:
> <CAKKCnfdU0w4mdLrmt5SbHYZTuXF01bHgTQ5yu5n-ejLaRnLt9g at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I think I figured it out...
>
> each time I run subprocess.Popen("command"), I also have to count += 1,
> which adds 1 to count each time the command is run. Is this correct, or is
> there a better way?
>
> Thanks
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