Re: [Tutor] If a method has no return type?

[Kal Sze]

Dear Sunil,

No method or function in Python has a *static* return type. That's
because Python is by nature a dynamic language, with duck typing and
dynamic dispatch. In fact, any method or function may well return any
of a number of different types:

def crazy_function(return_int)
if return_int:
return 1
else:
return 'foo'

It's probably bad design, but there is nothing in the Python grammar
and semantics that stops you from doing that.

So your question is better phrased as: if I don't explicitly return
anything, what is returned?

The answer to that would be: the None object

Cheers,
Kal

On 7 February 2013 14:09, Sunil Tech  wrote:
> If a method has no return type?
> what will it return?
>
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Re: [Tutor] unclear topic

[Kal Sze]

On 15 January 2013 05:19, Prasad, Ramit  wrote:
>
> Matthew Ngaha wrote:
> > hey guys, this is not really a Python question. When ever im doing a
> > tutorial, it could be pygame or some gui application, i usually find
> > everything straight forward until the demonstration involves drawing.
> > Then maths is applied and i can't follow along as easily. In the end
> > by commenting out certain lines of code, i understand what each line
> > is doing but the fact is im still faced with being very weak at
> > drawing and working out the logic behind it. I also can't imagine if
> > im designing a program and need to do drawings of my own how i would
> > work out the calculations and be able to think for myself. The help im
> > asking for is what do i need to study to be able to design my own
> > programs that involve drawing? do i need to go off and learn maths? if
> > so which type? some sort of geometry? or do i start studying some sort
> > of physics? or does the answer lie within some framework/library
> > python tutorial?
> >
> > on amazon ive seen:
> >
> > maths books
> > physics book
> > 2d engine physics books(box2d etc)
> > game physics books -  http://www.amazon.co.uk/Game-Physics-/dp/147103397X/
> >
> >
> > my other problem is i don't want to over do it. do i need to buy a
> > game physics book, if all i want to do is understand how to implement
> > my own calculations for complex objects etc? then again maybe that's
> > not so bad. If you know your way around this stuff? what did you learn
> > that gave you these skills?
>
> You should at least have enough math knowledge to understand Cartesian
> coordinates systems. Once you think of things in terms of objects
> based on their the coordinate location (x, y, z) it becomes easier
> to place objects where you want them and move them. Some trigonometry/
> algebra might also be helpful.
>
> I (personally) would not buy a game physics book unless you are
> looking to create a 3D game or a 2D game with an actual physics engine
> (e.g. World of Goo). Of course, this is based on my personal
> experience and education which may vastly vary from your own. Or,
> as they say "on them internets," YMMV.
>
>
> ~Ramit
>
>
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Hi Matthew,

Knowledge of Lineage Algebra is also invaluable. It forms the basis
for geometric transformations in 2D and 3D.

~Kal
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Re: [Tutor] New to Python - simple question

[Kal Sze]

On 18 November 2012 07:40, Alan Gauld  wrote:
> On 16/11/12 17:40, Unaiza Ahsan wrote:
>
>> There is a function created for histogram equalization of images (called
>> *histeq*), and saved in imtools.py.
>
>
>
> from PIL import Image
> from numpy import *
> im = array(Image.open('Tulips.jpg').convert('L'))
> im2,cdf = imtools.histeq(im)
>>
>>
>> I get this:
>>
>> Traceback (most recent call last):
>>  im2,cdf = imtools.histeq(im)
>>File "C:\Python27\imtools.py", line 18, in histeq
>>  imhist,bins = histogram(im.flatten(),nbr_bins,normed=True)
>> NameError: global name 'histogram' is not defined
>
>
> This tells us that the name histogram is not defined
> in the imtools.py file. Is it one of the modules ytou show imported above?
> If so it will not be visible inside imtools.py. You need to import the
> required module in that file too.
>
> But that's just a guess...
>
>
>> And the relevant portion in imtools.py is:
>> def histeq(im,nbr_bins=256):
>>  """ Histogram equalization of a grayscale image. """
>>
>>  #get image histogram
>>  imhist,bins = histogram(im.flatten(),nbr_bins,normed=True)
>
>
> This is the call, but where is histogram? If it is in imtools are you sure
> the spelling is correct? If its not there you need to import it from
> wherever it is defined.
>
> HTH
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
>
>
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Hi all,

The function histogram is supposed to come from the numpy module; at
least that's the case on my computer (I have numpy 1.6.2 for Python
2.7):

>>> from numpy import *
>>> histogram


Maybe something is wrong with Unaiza's version of numpy.

Kal
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Re: [Tutor] Scheme

[Kal Sze]

That's left as an exercise to the reader.

On Friday, August 31, 2012, Mark Lawrence wrote:

> On 31/08/2012 08:55, Alan Gauld wrote:
>
>>
>> Now just translate that into Scheme :-)
>>
>> HTH
>>
>>
> Anyone know of an application to automate Python to Scheme translation? :)
>
> --
> Cheers.
>
> Mark Lawrence.
>
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Re: [Tutor] Scheme

[Kal Sze]

And this looks like a homework problem, too.

It is against etiquette to just ask for the solution to homework on ANY
forum, message board, or mailing list. Since it's been given to you as
homework, you're supposed to give it enough thoughts, and (hopefully) come
up with your solution.

Even when you go to the Lisp or Scheme mailing list, you should at least
show what you have tried, paste your own code, and tell them where you are
stuck.

On 31 August 2012 07:32, Ashley Fowler  wrote:

>  This is a problem using the Scheme programming...Can anybody help me
> with this problem?
>
>  2. Write a procedure (sphere r) that takes the radius of a sphere
> as the value of its input parameter and returns the volume of that
> sphere given by the formula: (4/3)π(r^3). Use (require scheme/math)
> or (require racket/math) to load the math library containing the
> "pi" constant.
> Be sure to use "cube" from problem (1) to find the cube of r (r^3).
>
> Tests:
> (sphere 2)   ==> 33.51 ...
> (sphere 5.3) ==> 623.61 ...
>
>
>
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[Tutor] Prescriptive vs descriptive docstring

[Kal Sze]

Hello,

PEP 257 says that docstrings should be written in a prescriptive way (i.e.
using the imperative mood) instead of a descriptive way (indicative mood).
This seems like a rather odd recommendation. Since the docstring is
supposed to tell the programmer *how* to use a function/method, I've always
thought that a description in the indicative mood is appropriate. What's
the point in saying it like a command? Who are you "commanding" when what
you really want is to learn what the function/method does?

In Javadoc and XML doc (Java's and .NET's equivalent to docstrings), the
de-facto convention is to use the indicative mood (as can be seen in the
whole standard java class library and .net class library).

Is this difference somehow a corollary of the difference in programming
paradigms?

Was there a discussion in doc-...@python.org about the reason(s) to use the
imperative mood instead of the indicative mood, which then led to the
recommendation in PEP 257?

Best Regards,
Kal
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