[Tutor] Calculation error with a simple program
Hi everyone. I'm reading through a beginners Python book and came up
with a super simple program. I'm not getting any errors and everything
runs through, but there's a logical calculation error. What the program
does is take an amount and calculate a couple percentages and add a
couple fees.
For example, if I put in a value of 1, it will output 752.12 as the sub
total and 753.12 as the grand total. It's off by 1 on sub total and 2 on
grand total.
Thanks in advance! Jim Gallaher
# Car Salesman Calculator
# User enters the base price of the car and the program adds tax,
license, dealer prep, and destination charge.
print("Car Sales Calculator")
basePrice = int(input("Please enter in the price of the car: "))
# Misc charges to be added to the total cost of the car
tax = basePrice * .07
license = basePrice * .05
dealerPrep = basePrice + 500
destinationCharge = basePrice + 250
# Add the total misc charges together
subTotal = float(tax + license + dealerPrep + destinationCharge)
# Add all the misic charges and include the base price
grandTotal = float(subTotal + basePrice)
# Display the results
print("\nThe sub total is", subTotal)
print("\nYour grand Total is", grandTotal)
input("\nPress the enter key to close the program.")
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Re: [Tutor] Calculation error with a simple program
On 12/12/15 07:03, Jim Gallaher wrote:
> For example, if I put in a value of 1, it will output 752.12 as the sub
> total and 753.12 as the grand total. It's off by 1 on sub total and 2 on
> grand total.
Are you sure? Lets check the values...
> basePrice = int(input("Please enter in the price of the car: "))
=> 1
> tax = basePrice * .07
=> 0.07
> license = basePrice * .05
=> 0.05
> dealerPrep = basePrice + 500
=> 501
> destinationCharge = basePrice + 250
=> 251
> # Add the total misc charges together
> subTotal = float(tax + license + dealerPrep + destinationCharge)
=> 0.07 + 0.05 + 501 + 251 => 752.12
> # Add all the misic charges and include the base price
> grandTotal = float(subTotal + basePrice)
=> 752.12 + 1 => 753.12
Looks like Python got it right to me?
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
Follow my photo-blog on Flickr at:
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Re: [Tutor] Calculation error with a simple program
I haven't verified this, but you are probably up against some problem caused by using floating point to store money. The problem is that, when people see something like the floating point number, 3.15 they think, aha, this is a decimal number just like I learned in school when I was 10 years old. This is 3 plus one-tenth, plus 5 one hundreths. exactly. I know everything about this sort of thing, I learned it when I was 10. In particular, you probably learned this properly of numbers in general. (a + b) + c = a + (b + c) (associative properly of addition) And while you probably had not thought about this property, you definitely exepected it to work with your 3.15 when you want to add it to 2.17 And, herein lies the rub. floating point numbers, despite looking exactly the same as what you learned in school (A terrible design decision, I think that if we wrote them 3_15 or 3#15 we would have many fewer problems now, but it got made before I was born, so ) ARE NOT the things you learned in school. Not all decimal numbers are exactly representable in floating point. As a result the law of association fails. The correct result can indeed depend on the order in which you do your operations. You can read more about this here: https://docs.python.org/3.5/faq/design.html#why-are-floating-point-calculations-so-inaccurate and in the tutorial: https://docs.python.org/3.5/tutorial/floatingpoint.html#tut-fp-issues This is also good. http://floating-point-gui.de/ And if you want a more serious, mathematical approach, this ACM reprint is _really good_, but not to everybody's taste. https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html Most of the time, this does not matter, because most of the people using floating point are scientists. Scientists, contrary to popular belief, are not all that concerned with exact accuracy. Their results always come with an error estimate. 'the distance is such and such +/- 10%' or +/- 0.005% or what have you. So, as long as you do your calculations in such a way that the floating point error is covered in the % of uncertainty that you have anyway, your answer is perfectly correct enough for science. And floating calculations are much, much faster than fixed point decimal calculations, which in the old days meant the difference between getting a result for your calculations in a week or in more than a month. No wonder the scientists were happy to trade accuracy which they couldn't use for speed, which they had immediate need for. But once you get to calculations with money, you are suddenly out of the realm of science. (Even if some economists might want to tell you different. :) ) Money is exact. Nobody is willing to accept 10 pounds +/- 10% for a pizza, and allow people to pay anything between 9 pounds and 11 pounds as an ok price. In python we have a fix for this, called the Decimal object. Decimals behave the way you want them to -- i.e. the principle of associaton holds. https://docs.python.org/3.5/library/decimal.html So, if you are just noodling around, playing with things, using floats to store money is ok. It teaches bad habits, but that battle was fought and lost a long time ago. However, if you want to do something serious, like keep track of your own financial affairs with python, ***Don't Use Float For Money***. Please save yourself grief and use the Decimal type instead. Laura ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Calculation error with a simple program
On Sat, Dec 12, 2015 at 01:03:05AM -0600, Jim Gallaher wrote: > Hi everyone. I'm reading through a beginners Python book and came up > with a super simple program. I'm not getting any errors and everything > runs through, but there's a logical calculation error. What the program > does is take an amount and calculate a couple percentages and add a > couple fees. > > For example, if I put in a value of 1, it will output 752.12 as the sub > total and 753.12 as the grand total. It's off by 1 on sub total and 2 on > grand total. Check your arithmetic -- with a base price of $1, the sub total is $752.12 and the grand total is $753.12, exactly as Python calculates. But I wonder whether you have made a logic mistake in your code. You say: dealerPrep = basePrice + 500 destinationCharge = basePrice + 250 This means that the car will cost more than TRIPLE the base price. Instead of $1, enter a base price of $40,000 and you will see what I mean: now the dealer prep is $40500 and the destination charge is $40250, which added to the base price gives $120750 (plus tax and licence). Surely that's not right, the deal charges more than the cost of the car for preparation? I think what you want is: dealerPrep = 500 destinationCharge = 250 -- Steve ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Calculation error with a simple program
Hi Alan, I'm 100 percent sure I'm wrong. :-) I verified it when I fixed the mistake. The problem was it was adding in the basePrice and the fixed rates/percentages each time. So I figured it out when Ian said something about that. Thanks for everyone's help! :-) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Calculation error with a simple program
> On Dec 12, 2015, at 2:03 AM, Jim Gallaher wrote:
>
> Hi everyone. I'm reading through a beginners Python book and came up with a
> super simple program. I'm not getting any errors and everything runs through,
> but there's a logical calculation error. What the program does is take an
> amount and calculate a couple percentages and add a couple fees.
>
> For example, if I put in a value of 1, it will output 752.12 as the sub total
> and 753.12 as the grand total. It's off by 1 on sub total and 2 on grand
> total.
>
> Thanks in advance! Jim Gallaher
>
> # Car Salesman Calculator
>
> # User enters the base price of the car and the program adds tax, license,
> dealer prep, and destination charge.
>
> print("Car Sales Calculator")
> basePrice = int(input("Please enter in the price of the car: "))
>
> # Misc charges to be added to the total cost of the car
> tax = basePrice * .07
> license = basePrice * .05
> dealerPrep = basePrice + 500
> destinationCharge = basePrice + 250
>
I think your main problem is right here. Why do dealerPrep and
destinationCharge include the basePrice in their equation? This will add the
basePrice in multiple times. I would simply set it like this:
dealerPrep = 500
destinationCharge = 250
If these charges ever change, you can put in some sort of equation. However, it
looks like these are meant to be a flat fee.
> # Add the total misc charges together
> subTotal = float(tax + license + dealerPrep + destinationCharge)
>
> # Add all the misic charges and include the base pricem
> grandTotal = float(subTotal + basePrice)
>
> # Display the results
> print("\nThe sub total is", subTotal)
> print("\nYour grand Total is", grandTotal)
>
> input("\nPress the enter key to close the program.")
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> Tutor maillist - Tutor@python.org
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Re: [Tutor] Tutor Digest, Vol 142, Issue 10
I have a more simple-minded solution. The error appears to occur in testing
without revealing the problem by use of $1 base price in the test. Using
$10,000 as the base price in the test reveals absurd numbers. I think the real
problem lies in the inclusion of base price inappropriately, twice as in:
>dealerPrep = basePrice + 500
>destinationCharge = basePrice + 250
"basePrice" has no place in those two lines. 500 and 250 alone express the
definition of the challenge.
Ken
In , on 12/12/15
at 12:00 PM, tutor-requ...@python.org said:
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>Today's Topics:
> 1. Calculation error with a simple program (Jim Gallaher)
> 2. Re: Calculation error with a simple program (Alan Gauld)
> 3. Re: Calculation error with a simple program (Laura Creighton)
>--
>Message: 1
>Date: Sat, 12 Dec 2015 01:03:05 -0600
>From: Jim Gallaher
>To: tutor@python.org
>Subject: [Tutor] Calculation error with a simple program
>Message-ID: <566bc6a9.6090...@gmail.com>
>Content-Type: text/plain; charset=utf-8; format=flowed
>Hi everyone. I'm reading through a beginners Python book and came up with
>a super simple program. I'm not getting any errors and everything runs
>through, but there's a logical calculation error. What the program does is
>take an amount and calculate a couple percentages and add a couple fees.
>For example, if I put in a value of 1, it will output 752.12 as the sub
>total and 753.12 as the grand total. It's off by 1 on sub total and 2 on
>grand total.
>Thanks in advance! Jim Gallaher
># Car Salesman Calculator
># User enters the base price of the car and the program adds tax, license,
>dealer prep, and destination charge.
>print("Car Sales Calculator")
>basePrice = int(input("Please enter in the price of the car: "))
># Misc charges to be added to the total cost of the car
>tax = basePrice * .07
>license = basePrice * .05
>dealerPrep = basePrice + 500
>destinationCharge = basePrice + 250
># Add the total misc charges together
>subTotal = float(tax + license + dealerPrep + destinationCharge)
># Add all the misic charges and include the base price
>grandTotal = float(subTotal + basePrice)
># Display the results
>print("\nThe sub total is", subTotal)
>print("\nYour grand Total is", grandTotal)
>input("\nPress the enter key to close the program.")
>--
>Message: 2
>Date: Sat, 12 Dec 2015 08:04:52 +
>From: Alan Gauld
>To: tutor@python.org
>Subject: Re: [Tutor] Calculation error with a simple program
>Message-ID:
>Content-Type: text/plain; charset=utf-8
>On 12/12/15 07:03, Jim Gallaher wrote:
>> For example, if I put in a value of 1, it will output 752.12 as the sub
>> total and 753.12 as the grand total. It's off by 1 on sub total and 2 on
>> grand total.
>Are you sure? Lets check the values...
>> basePrice = int(input("Please enter in the price of the car: "))
>=> 1
>> tax = basePrice * .07
>=> 0.07
>> license = basePrice * .05
>=> 0.05
>> dealerPrep = basePrice + 500
>=> 501
>> destinationCharge = basePrice + 250
>=> 251
>> # Add the total misc charges together
>> subTotal = float(tax + license + dealerPrep + destinationCharge)
>=> 0.07 + 0.05 + 501 + 251 => 752.12
>> # Add all the misic charges and include the base price
>> grandTotal = float(subTotal + basePrice)
>=> 752.12 + 1 => 753.12
>Looks like Python got it right to me?
--
---
K.F.Hammer Associates Ken Hammer
management consultations Saint Johnsbury, VT 05819
---
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[Tutor] Beautiful Soup
Dear All,
I am trying to scrap the following website, however, I have
encountered some problems. As you can see, I am not really familiar
with regex and I hope you can give me some pointers to how to solve
this problem.
I hope I can download all the transaction data into the database.
However, I need to retrieve it first. The data which I hope to
retrieve it is as follows:
"
15:59:59 A 500 6.790 3,395
15:59:53 B 500 6.780 3,390
Thank you
Below is my quote:
from bs4 import BeautifulSoup
import requests
import re
url =
'https://bochk.etnet.com.hk/content/bochkweb/eng/quote_transaction_daily_history.php?code=6881&time=F&timeFrom=09&timeTo=16&turnover=S&sessionId=44c99b61679e019666f0570db51ad932&volMin=0&turnoverMin=0'
def turnover_detail(url):
response = requests.get(url)
html = response.content
soup = BeautifulSoup(html,"html.parser")
data = soup.find_all("script")
for json in data:
print(json)
turnover_detail(url)
Best Regards,
Henry
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