Re: [Tutor] Alternating patterns
kevin parks wrote: >>From: Kent Johnson <[EMAIL PROTECTED]> >>itertools.cycle() will repeat a sequence indefinitely: >>In [2]: from itertools import cycle >> >>In [3]: i=cycle([1,2]) >> >>In [5]: for j in range(6): >>...: print i.next() >>...: >>...: >>1 >>2 >>1 >>2 >>1 >>2 >> >>For non-repeating sequences I would look at writing a generator >>function >>for the sequences. >> >>Kent > > okay.. i am painfully unaware of generators, iterators, sets, genexes > and a lot of the new stuff post 2.3 & 2.4 stuffs... my problem is that > i find the online docs kind of terse and few of the Python books yet > cover these newer constructs in detail > > itertools looks very cool are there any toots on the above and on > Sets & itertools? It really seems like it would help to know these for > my work... That liddo bit right up there with itertools.cycle already > has me a drooling... (so helpful that would be!) The best introduction to new features is usually in the What's New document accompanying the release where the feature was added. Of course it helps to know when the feature was added...here are some generator examples: http://www.python.org/doc/2.2.3/whatsnew/node5.html Generators are excellent for encapsulating the generation of a sequence when there is state that must be maintained between elements. For example here is a generator that takes a sequence argument, and yields this sequence of sequences: the original sequence the original sequence with the first element incremented by one the original sequence the original sequence with the second element incremented by one etc until each element has been incremented In [2]: def change_each(seq): ...: seq = list(seq) # Copy and ensure it's a list ...: for i in range(len(seq)): ...: yield seq ...: seq[i] += 1 ...: yield seq ...: seq[i] -= 1 ...: ...: In [3]: s = [1, 3] In [5]: for n in change_each(s): ...: print n ...: ...: [1, 3] [2, 3] [1, 3] [1, 4] If you wanted to repeat this sequence indefinitely you could just wrap it with itertools.cycle(). The module docs for itertools contain quite a few examples: http://docs.python.org/lib/itertools-recipes.html itertools.cycle() is pretty simple, it just loops endlessly over the sequence you give it. The itertools docs shows equivalent Python functions for each of the itertools functions. Most of them are implemented using generator functions so by looking at them you can learn about itertools and generators at the same time. http://docs.python.org/lib/itertools-functions.html Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Alternating patterns
Hi,you can also use simple way of iterating using modus: L = [1,2] for i in range(6): print L[i%len(L)]121212Cheers,pujo On 3/29/06, kevin parks <[EMAIL PROTECTED]> wrote: >>>> -->> Message: 10> Date: Tue, 28 Mar 2006 22:43:38 -0500> From: Kent Johnson <[EMAIL PROTECTED]> > Subject: Re: [Tutor] Alternating patterns> Cc: tutor@python.org> Message-ID: <[EMAIL PROTECTED]>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed >> kevin parks wrote:>> I have a set that i iterate over... but each time through it i would>> like to alternate between the original set and a variation of the set>> that has one of the members of the set altered (by + or - 1) >>>> So if my original set is:>>>> [0, 2, 4, 5, 7, 9, 11]>>>> I would use that the first pass but on the second pass i might like>> the third member (4,) to become 3, (-1) resulting in : [0, 2, 3, 5, 7, >> 9, 11]>>>> But then back again to the original on the next pass (+1 back to 4,):>> [0, 2, 4, 5, 7, 9, 11]>>>> and then back: [0, 2, 3, 5, 7, 9, 11] again, etc. >>> How can one make such alternating patterns?>> itertools.cycle() will repeat a sequence indefinitely:> In [2]: from itertools import cycle>> In [3]: i=cycle([1,2]) >> In [5]: for j in range(6):> ...: print i.next()> ...:> ...:> 1> 2> 1> 2> 1> 2>> For non-repeating sequences I would look at writing a generator > function> for the sequences.>> Kentokay.. i am painfully unaware of generators, iterators, sets, genexesand a lot of the new stuff post 2.3 & 2.4 stuffs... my problem is that i find the online docs kind of terse and few of the Python books yetcover these newer constructs in detailitertools looks very cool are there any toots on the above and onSets & itertools? It really seems like it would help to know these for my work... That liddo bit right up there with itertools.cycle alreadyhas me a drooling... (so helpful that would be!)-kp--___Tutor maillist - Tutor@python.orghttp://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Alternating patterns
> > > > -- > > Message: 10 > Date: Tue, 28 Mar 2006 22:43:38 -0500 > From: Kent Johnson <[EMAIL PROTECTED]> > Subject: Re: [Tutor] Alternating patterns > Cc: tutor@python.org > Message-ID: <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > kevin parks wrote: >> I have a set that i iterate over... but each time through it i would >> like to alternate between the original set and a variation of the set >> that has one of the members of the set altered (by + or - 1) >> >> So if my original set is: >> >> [0, 2, 4, 5, 7, 9, 11] >> >> I would use that the first pass but on the second pass i might like >> the third member (4,) to become 3, (-1) resulting in : [0, 2, 3, 5, 7, >> 9, 11] >> >> But then back again to the original on the next pass (+1 back to 4,): >> [0, 2, 4, 5, 7, 9, 11] >> >> and then back: [0, 2, 3, 5, 7, 9, 11] again, etc. > >> How can one make such alternating patterns? > > itertools.cycle() will repeat a sequence indefinitely: > In [2]: from itertools import cycle > > In [3]: i=cycle([1,2]) > > In [5]: for j in range(6): > ...: print i.next() > ...: > ...: > 1 > 2 > 1 > 2 > 1 > 2 > > For non-repeating sequences I would look at writing a generator > function > for the sequences. > > Kent okay.. i am painfully unaware of generators, iterators, sets, genexes and a lot of the new stuff post 2.3 & 2.4 stuffs... my problem is that i find the online docs kind of terse and few of the Python books yet cover these newer constructs in detail itertools looks very cool are there any toots on the above and on Sets & itertools? It really seems like it would help to know these for my work... That liddo bit right up there with itertools.cycle already has me a drooling... (so helpful that would be!) -kp-- ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Alternating patterns
kevin parks wrote: > I have a set that i iterate over... but each time through it i would > like to alternate between the original set and a variation of the set > that has one of the members of the set altered (by + or - 1) > > So if my original set is: > > [0, 2, 4, 5, 7, 9, 11] > > I would use that the first pass but on the second pass i might like > the third member (4,) to become 3, (-1) resulting in : [0, 2, 3, 5, 7, > 9, 11] > > But then back again to the original on the next pass (+1 back to 4,): > [0, 2, 4, 5, 7, 9, 11] > > and then back: [0, 2, 3, 5, 7, 9, 11] again, etc. > How can one make such alternating patterns? itertools.cycle() will repeat a sequence indefinitely: In [2]: from itertools import cycle In [3]: i=cycle([1,2]) In [5]: for j in range(6): ...: print i.next() ...: ...: 1 2 1 2 1 2 For non-repeating sequences I would look at writing a generator function for the sequences. Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
[Tutor] Alternating patterns
I have a set that i iterate over... but each time through it i would like to alternate between the original set and a variation of the set that has one of the members of the set altered (by + or - 1) So if my original set is: [0, 2, 4, 5, 7, 9, 11] I would use that the first pass but on the second pass i might like the third member (4,) to become 3, (-1) resulting in : [0, 2, 3, 5, 7, 9, 11] But then back again to the original on the next pass (+1 back to 4,): [0, 2, 4, 5, 7, 9, 11] and then back: [0, 2, 3, 5, 7, 9, 11] again, etc. in other words i would like to alternate members of the set back and forth. Usually only 1 (or sometimes 2,) member at time. i could also imagine a needing(alter one, alter another, undo that, undo the first back to the original set): [0, 2, 4, 5, 7, 9, 11] --> [0, 2, 3, 5, 7, 9, 11] --> [0, 2, 3, 5, 7, 8, 10] --> [0, 2, 3, 5, 7, 9, 11] --> [0, 2, 4, 5, 7, 9, 11] or: original --> [0, 2, 4, 5, 7, 9, 11] altered --> [0, 2, 3, 5, 7, 9, 11] now back to 4, but change something else (like 11, is now 10): [0, 2, 4, 5, 7, 9, 10] etc... How can one make such alternating patterns? -kp-- ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
