Re: [Tutor] A couple newbie questions about Python
-Original Message- From: breamore...@yahoo.co.uk Sent: Thu, 12 Jun 2014 09:18:16 +0100 To: tutor@python.org Subject: Re: [Tutor] A couple newbie questions about Python Please don't top post, it makes following a long thread extremely difficult, thanks. sorry. The other python list wants you to, so I just assumed... Deb in WA, USA She says as she almost top posts again :P... FREE 3D MARINE AQUARIUM SCREENSAVER - Watch dolphins, sharks orcas on your desktop! Check it out at http://www.inbox.com/marineaquarium ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
Thanks very much Alan. As for the my concern about inaccuracy in float math, I suppose I am concerned because I was not aware of the issue before, and I wonder how you deal with such things when you need accuracy for financial things. Deb in WA, USA -Original Message- From: alan.ga...@btinternet.com Sent: Wed, 11 Jun 2014 23:48:37 +0100 To: tutor@python.org Subject: Re: [Tutor] A couple newbie questions about Python On 11/06/14 21:46, Deb Wyatt wrote: Hi. Everywhere I have read, the 'standard practice' for indentation is 4 spaces, That's a style recommendation. Python doesn't care. But your readers will. 2 spaces is the absolute minimum, 8 spaces is about the absolute maximum. Outside that it gets hard to read the code. 3, 4 or 5 spaces is pretty good and you are unlikely to get complaints except from style pedants or if you are submitting code for the standard library where they like to stick with the official guidance. I just recently became aware of the inaccuracy of calculations using floats and I am concerned about that. The inaccuracies are an inevitable result of the way your computer processes floating point numbers. In what way are you concerned? Its not a Python issue - the exact same issues occur in any computer - or even your pocket calculator. If it concerns you in Excel or in Visual Basic/Java/C++ etc too then the good news is that Python has alternative renderings that can often reduce/eliminate them - but at the cost of speed and complexity. HTH -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor Protect your computer files with professional cloud backup. Get PCRx Backup and upload unlimited files automatically. Learn more at http://backup.pcrx.com/mail ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
I wonder how you deal with such things when you need accuracy for financial things. Financial applications traditionally work in the lowest unit of currency and use integers. For display purposes they convert the pennies into dollars/cents or pounds/pence or whatever. Alan Gauld Author of the Learn To Program website http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
Please don't top post, it makes following a long thread extremely difficult, thanks. On 12/06/2014 03:47, Deb Wyatt wrote: Thanks very much Alan. As for the my concern about inaccuracy in float math, I suppose I am concerned because I was not aware of the issue before, and I wonder how you deal with such things when you need accuracy for financial things. Deb in WA, USA Besides Alan's previous statement about using integers you can also use things like Python's decimal module see https://docs.python.org/3/library/decimal.html#module-decimal -- My fellow Pythonistas, ask not what our language can do for you, ask what you can do for our language. Mark Lawrence --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
On Thu, Jun 12, 2014 at 1:27 AM, Alex Kleider aklei...@sonic.net wrote: On 2014-06-11 20:08, Dave Angel wrote: I learned programming in 1967 with Fortran, and McCracken spent a chapter warning about that same thing. Probably everything he warned about still applies to Python and modern computers. A google search for McCracken did not yield anyone that seems to fit the person you reference. Can you clarify, please? 1961 A Guide to Fortran Programming openlibrary.org/works/OL4628575W 1964 Numerical Methods and Fortran Programming openlibrary.org/books/OL5914708M 1965 A Guide to Fortran IV Programming openlibrary.org/books/OL5953402M 1967 Fortran with Engineering Applications openlibrary.org/books/OL5539818M snippets: books.google.com/books?id=qQY_IAAJdq=editions:STANFORD36105002062847 1974 A Simplified Guide to Fortran Programming openlibrary.org/works/OL4628579W 1972 Numerical Methods with Fortran IV Case Studies openlibrary.org/books/OL4559608M 1984 Computing for Engineers and Scientists with Fortran 77 openlibrary.org/books/OL3180840M ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
On 12/06/14 09:18, Mark Lawrence wrote: Besides Alan's previous statement about using integers you can also use things like Python's decimal module see https://docs.python.org/3/library/decimal.html#module-decimal Although Decimal doesn't solve the issue of rounding errors for financial calculations (neither do pennies) nor the issues of repeating results like 1/7 It just moves them into the more familiar territory of decimal numbers rather than binary. So at least what you write is represented accurately. As Steven said in his reply, floating point on computers is hard. -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
On 11/06/14 21:46, Deb Wyatt wrote: Hi. Everywhere I have read, the 'standard practice' for indentation is 4 spaces, That's a style recommendation. Python doesn't care. But your readers will. 2 spaces is the absolute minimum, 8 spaces is about the absolute maximum. Outside that it gets hard to read the code. 3, 4 or 5 spaces is pretty good and you are unlikely to get complaints except from style pedants or if you are submitting code for the standard library where they like to stick with the official guidance. I just recently became aware of the inaccuracy of calculations using floats and I am concerned about that. The inaccuracies are an inevitable result of the way your computer processes floating point numbers. In what way are you concerned? Its not a Python issue - the exact same issues occur in any computer - or even your pocket calculator. If it concerns you in Excel or in Visual Basic/Java/C++ etc too then the good news is that Python has alternative renderings that can often reduce/eliminate them - but at the cost of speed and complexity. HTH -- Alan G Author of the Learn to Program web site http://www.alan-g.me.uk/ http://www.flickr.com/photos/alangauldphotos ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
Deb Wyatt codemon...@inbox.com Wrote in message: Hi. Everywhere I have read, the 'standard practice' for indentation is 4 spaces, but I am running into 2 space indentation in a lot of tutorials and such. Should I keep with the 4 spaces, or does it even matter, as long as it is consistent? 4 spaces is an excellent choice in my opinion, and many other people's. We just tell our editor to turn the tab key into 4 column alignment and pretty much forget about it. The python interpreter doesn't care. But other people's opinions will matter as soon as you share your code, or work on a multi person project. Note that when you're looking at other people's code, you may be seeing it differently than they, chief reason being html (thank you for remembering to post here in text). The other reason you may think they're using 2 is proportional spacing. It should be off for code. I just recently became aware of the inaccuracy of calculations using floats and I am concerned about that. I learned programming in 1967 with Fortran, and McCracken spent a chapter warning about that same thing. Probably everything he warned about still applies to Python and modern computers. It is impossible to do serious computing for long without running into these issues. But Python has as many ways of avoiding them as any mainstream language. You can use decimal to avoid some types of problems, and fractions to avoid others. And common sense for others. You will need to understand your tools. BTW, calculators and spreadsheets frequently use decimal rather than binary, and I wrote a decimal floating package for a computer in the mid 70's. It didn't even offer binary. -- DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
Hi Deb, My responses below, interleaved with your questions. On Wed, Jun 11, 2014 at 12:46:11PM -0800, Deb Wyatt wrote: Hi. Everywhere I have read, the 'standard practice' for indentation is 4 spaces, but I am running into 2 space indentation in a lot of tutorials and such. Should I keep with the 4 spaces, or does it even matter, as long as it is consistent? Four spaces is common, and recommended by PEP 8, which describes the coding styles for the Python standard library: https://www.python.org/dev/peps/pep-0008 But it's not compulsory (except for contributions to the standard library). There are good reasons for sticking to four spaces, but eight spaces or a single tab are also common. In my opinion, two spaces is too little, and one space is right out. But as far as the Python interpreter is concerned, it doesn't care, so long as you're consistent. (However, other people reading your code may care.) I just recently became aware of the inaccuracy of calculations using floats and I am concerned about that. Floating point mathematics is tricky. What you're seeing is not a bug in Python, but a general problem with floating point calculations in general. Regardless of whether you use Python, or C, or Java, or some other programming language, you have to face the same issues that calculations with floats are not always accurate compared to what you expect from pure mathematics. (Think about your calculator: how often do you get a number like 3.001 instead of 3, or 0.499 instead of 0.5?) You can read up on some of the issues here: http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html although it's quite technical. Some less technical discussions can be found here: http://randomascii.wordpress.com/2012/04/05/floating-point-complexities/ http://support.microsoft.com/kb/42980 but however you look at it, it's complicated, and inherent to the problem, not the fault of Python. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
On 2014-06-11 20:08, Dave Angel wrote: I learned programming in 1967 with Fortran, and McCracken spent a chapter warning about that same thing. Probably everything he warned about still applies to Python and modern computers. A google search for McCracken did not yield anyone that seems to fit the person you reference. Can you clarify, please? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] A couple newbie questions about Python
Hi, responses below...
Dne 11. 6. 2014 22:46, Deb Wyatt napsal(a):
Hi. Everywhere I have read, the 'standard practice' for indentation is 4
spaces, but I am running into 2 space indentation in a lot of tutorials and
such. Should I keep with the 4 spaces, or does it even matter, as long as it
is consistent?
I recommend to use ammount of spaces that is consistent with already
existing project.
If it is a new project, use whatever you like - 4 spaces is recommended
(looks good :)
I just recently became aware of the inaccuracy of calculations using floats and
I am concerned about that.
If there are numerical operations where precision is necessary
(accounting or banking) use decimal type
from decimal import Decimal
a = Decimal('0.1')
b = Decimal('0.9')
print a + b
Note these numbers are passed to Decimal as a string, that is for a
reason - if you pass float to Decimal, it will already loose precision
and the whole thing doesn't make sense - and aslo will throw an exception.
I am using Python 3, just fyi.
Thanks for any enlightenment on these questions.
Deb in WA, USA
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Lukas
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