[Tutor] Need help with generators....
I am doing "Building Skills in Python". In the Generator Function example at [url] http://www.itmaybeahack.com/homepage/books/python/html/p02/p02c08_generators.html#generator-function-example[/url]i can't understand, how it is working properly. what i understood is as follows:> 1)First it makes count = 0 2)then it goes straight in for loop 3)Since the first color is red, it goes in else block and increment count to 1 and stop execution. 4)Now its next method is called using list comprehension, and it resumes its execution and yield its first value i.e. 1.Note that the yield statement is outside the for loop. 5)Now there is no further yield statement which can stop execution of countreds() function.So it raises StopExecution exception But this is not what is happening. why? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Need help with generators....
On 15/02/14 13:35, Bunny Sehgal wrote:
I am doing "Building Skills in Python". In the Generator Function
example at
I assume you are talking about this one:
spins = [('red', '18'), ('black', '13'), ('red', '7'),
('red', '5'), ('black', '13'), ('red', '25'),
('red', '9'), ('black', '26'), ('black', '15'),
('black', '20'), ('black', '31'), ('red', '3')]
def countReds( aList ):
count= 0
for color,number in aList:
if color == 'black':
yield count
count= 0
else:
count += 1
yield count
gaps= [ gap for gap in countReds(spins) ]
print gaps
what i understood is as follows:>
1)First it makes count = 0
2)then it goes straight in for loop
3)Since the first color is red, it goes in else block and increment
count to 1 and stop execution.
What makes you think it stops?
It carries on to the next iteration which is black and so enters the if
block which yields the count which will be 1.
4)Now its next method is called using list comprehension, and it resumes
its execution and yield its first value i.e. 1.Note that the yield
statement is outside the for loop.
Not quite,
Next time round it carries on from the yield so sets count back
to zero and fetches the next two tuples before hitting another
black. So this time it yields 2.
Once the tuples are exhausted it yields the final count,
which should be 1
5)Now there is no further yield statement which can stop execution of
countreds() function.So it raises StopExecution exception
But this is not what is happening. why?
Your understanding was flawed. Assuming I've pasted the correct code
listing... But there is an explanation right under the listing on the
page. Assuming you read it, which bit of that did you not understand?
HTH
--
Alan G
Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.flickr.com/photos/alangauldphotos
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Re: [Tutor] thanks - Beginner - explaining 'Flip a coin' bug
Hi David, Thanks for your input about the logic of this little script of mine. I confess I omitted the edge possibility and assumed heads or taisl only. As I progress further with getting the foundation knowledge of the language itself, it is really appreciated to be corrected on what good programming is about regardless of the language. Please keep commenting/helping whenever necessary. Cheers, Marc Date: Fri, 14 Feb 2014 22:49:43 -0500 Subject: Re: [Tutor] Beginner - explaining 'Flip a coin' bug From: dwightdhu...@gmail.com To: marc_eym...@hotmail.com CC: tutor@python.org Here is a problem I've come across, from empirical evidence, that also relates to your equation. We always assume that their are always two probabilities, that a coin can be either head or tails. However, there are dynamics within a third realm of the dimensionality of the coin...it's not a two dimensional plane. So the planar probabilities in relation to the 'surface are' hold another possibility...the 'edge'. The algorithm of applying the edge are up to you, but I've seen the coin land on it's curved edge more than once, so this function you've designed, should have more than two possibilities, within a complete algorithm to the real world functionality of the coin in question. On Wed, Feb 12, 2014 at 10:25 AM, Marc Eymard wrote: Hello there, I want to emulate a coin flip and count how many heads and tails when flipping it a hundred times. I first coded coinflip_WRONG.py with "count_flips += 1" statement within the if/else block. When running it, either returned values are wrong or the script seems to enter in an infinite loop showing no return values at all. coinflip.py is a corrected version I worked out myself. I moved "count_flips+= 1" out of if/else block and inserted it before if/else. However, I still don't understand the bug since, in my understanding, both files are incrementing variable count_flips each time until the loop becomes false. Can somebody explain the reason of the bug. Cheers, Marc ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor -- Best Regards, David Hutto CEO: http://www.hitwebdevelopment.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Beginner - understanding randint arguments
Hello Tutor, I need to generate a random integer between 0 and 100. The range is supposed to be adjusted by my two variables: low_range and high_range. The logic of using the variables as part of the function arguments is to manage to get a smaller range each time the function is called excluding the possible repeat of the return value of randint. Here is what happens in my script: >>> import random >>> low_range = -1 >>> high_range = 101 >>> random.randint(low_range + 1, high_range - 1) 56 >>> low_range -1 >>> high_range 101 I was rather expecting: >>> low_range 0 >>> high_range 100 Can somebody explain why both low_range and high_range are still returning their initial values ? Thanks, Marc ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Beginner - understanding randint arguments
On 02/15/2014 11:25 AM, Marc Eymard wrote: Hello Tutor, I need to generate a random integer between 0 and 100. The range is supposed to be adjusted by my two variables: low_range and high_range. The logic of using the variables as part of the function arguments is to manage to get a smaller range each time the function is called _excluding_ the possible repeat of the return value of randint. Here is what happens in my script: >>> import random >>> low_range = -1 >>> high_range = 101 >>> random.randint(low_range + 1, high_range - 1) 56 >>> low_range -1 >>> high_range 101* * I was rather expecting: >>> low_range 0 >>> high_range 100 Can somebody explain why both low_range and high_range are still returning their initial values ? Thanks, Marc* * The variables low_range and high_range are not modified. The arguments to random.randint do not change the initial values of the variables, only the actual values passed. -- Jay Lozier jsloz...@gmail.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Beginner - understanding randint arguments
On 15/02/14 16:25, Marc Eymard wrote: Here is what happens in my script: >>> import random >>> low_range = -1 >>> high_range = 101 >>> random.randint(low_range + 1, high_range - 1) 56 >>> low_range -1 >>> high_range 101* I was rather expecting: >>> low_range 0 >>> high_range 100 Really? Why? You never change low_range or high_range so why would their values change? The help() for randint says: randint(self, a, b) method of random.Random instance Return random integer in range [a, b], including both end points. So the function doesn't change the values either it just returns a random number between them. Can somebody explain why both low_range and high_range are still returning their initial values ? Because you didn't change them. When you called randint you passed in two expressions: low_range+1 and high_range-1 which Python evaluated as 0 and 100. But that did not change your variable values in any way, it just created new values that were passed into randint() as 'a' and 'b' respectively. -- 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] Beginner - understanding randint arguments
On Sat, Feb 15, 2014 at 04:25:34PM +, Marc Eymard wrote: > Can somebody explain why both low_range and high_range are still > returning their initial values ? Because you haven't changed either of them. Imagine the chaos if every time you did arithmetic on a variable, Python changed the variable: x = 1 y = x + 100 What is the value of y? 101, correct? What is the value of x? It should still be 1, not 101. The same applies when you get rid of the "y =" and just pass it to a function: x = 1 some_function(x + 100) What's the value of x? It needs to be 1, because you haven't changed it. The only way to change x is to explicitly change it: x = x + 100 -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Regular expressions
Thank you all.
On Thu, Feb 13, 2014 at 10:47 PM, Walter Prins wrote:
> Hi,
>
> On 13 February 2014 06:44, Santosh Kumar wrote:
> > I am using ipython.
> >
> > 1 ) Defined a string.
> >
> > In [88]: print string
> > foo foobar
> >
> > 2) compiled the string to grab the "foo" word.
> >
> > In [89]: reg = re.compile("foo",re.IGNORECASE)
> >
> > 3) Now i am trying to match .
> >
> > In [90]: match = reg.match(string)
> >
> > 4) Now i print it.
> >
> > In [93]: print match.group()
> > foo
> >
> > Correct me if i am wrong, i am expecting both "foo" and "foobar", why is
> it
> > giving
> > just "foo"
>
> A small addition to Peter's already comprehensive reply: Your regular
> expression is not including what follows "foo", it is defined as
> *only* the string literal "foo", so it can only ever match and return
> the literal string "foo".
>
> Try specifying "foo.*" as the regular expression. Example session:
>
> Python 2.7.5 (default, May 15 2013, 22:43:36) [MSC v.1500 32 bit (Intel)]
> Type "copyright", "credits" or "license" for more information.
>
> IPython 1.0.0 -- An enhanced Interactive Python.
> ? -> Introduction and overview of IPython's features.
> %quickref -> Quick reference.
> help -> Python's own help system.
> object? -> Details about 'object', use 'object??' for extra details.
>
> [C:/Src]|1> s='foo foobar'
>
> [C:/Src]|2> import re
>
> [C:/Src]|3> reg=re.compile('foo.*', re.IGNORECASE)
>
> [C:/Src]|4> match=reg.match(s)
>
> [C:/Src]|5> print match.group()
> foo foobar
>
>
>
> Walter
>
--
D. Santosh Kumar
RHCE | SCSA
+91-9703206361
Every task has a unpleasant side .. But you must focus on the end result
you are producing.
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