Reverse a String?

[Gregory Piñero]

Is my mind playing tricks on me? I really remember being able to
reverse a string as in:

text='greg'
print text.reverse()
>> 'gerg'

Is it possible thats in some Python install and not in others? I just
switched to linux.

In any case, can we get that added?

Here's my workaround for now:
def reverse(text):
return ''.join([text[i] for i in range(len(text)-1,-1,-1)])

--
Gregory Piñero
Chief Innovation Officer
Blended Technologies
(www.blendedtechnologies.com)

[Robert Kern]

Gregory Piñero wrote:
> Is my mind playing tricks on me? I really remember being able to
> reverse a string as in:
>
> text='greg'
> print text.reverse()
>>> 'gerg'
>
> Is it possible thats in some Python install and not in others? I just
> switched to linux.
>
> In any case, can we get that added?

Not in that form, no, since this already exists:

text[::-1]

--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco

[Leif K-Brooks]

Gregory Pińero wrote:
> Is my mind playing tricks on me? I really remember being able to
> reverse a string as in:
>
> text='greg'
> print text.reverse()
>>> 'gerg'

That method has never existed AFAIK. Maybe you're thinking of the
reverse() method on lists?

In any case, the you can reverse strings in a couple of ways:

>>> ''.join(reversed('foo'))
'oof'
>>> 'foo'[::-1]
'oof'

[p.la...@ieee.org]

That 'foo'[::-1] is the Python reverse string idiom I'll try here
forward, thanks.

Also '.h.e.l.l.o'[1::2] to pick out every second char, etc., thanks.

Three footnotes:

1) Reverse string isn't yet in http://www.python.org/doc/faq/

2) Google Groups searches here yesterday instead pushed me towards the
less concise:

def reverse(chars):
aa = array.array('c', chars)
aa.reverse()
return aa.tostring()

3) I went looking when first I found time to rethink what I had been
running this past year:

def reverse(chars):
ochars = ''
beyond = len(chars)
for ix in range(beyond):
ochars += chars[beyond - 1 - ix]
return ochars

[Gregory Piñero]

On 9/23/06, Robert Kern <rober...@gmail.com> wrote:
> Not in that form, no, since this already exists:
>
> text[::-1]

Wow, that's really cool! Here are my questions:

1. How long has this thing been going on? I didn't know slice even
took an extra argument like that.

2. Where can I get the lowdown on everything there is to know about
slice? Since I've obviously been living in ignorance all these years!

Thanks again,

Greg

[Robert Kern]

Gregory Piñero wrote:
> On 9/23/06, Robert Kern <rober...@gmail.com> wrote:
>> Not in that form, no, since this already exists:
>>
>> text[::-1]
>
> Wow, that's really cool! Here are my questions:
>
> 1. How long has this thing been going on? I didn't know slice even
> took an extra argument like that.

Slicing took that "step" argument since 1.4. However, only Numeric arrays used
it up until 2.3 where it was added to the builtin types.

> 2. Where can I get the lowdown on everything there is to know about
> slice? Since I've obviously been living in ignorance all these years!

http://www.python.org/doc/2.3.5/whatsnew/section-slices.html

Generally the "What's New" documents are very good for catching up. I've found
that they're also a very good, high-density method of refreshing one's memory
about useful little tidbits. Sadly, they're not all collected in one place for
that purpose. But you can fake it a bit by replacing <version> in the following
URL with each of 2.2.3, 2.3.5, 2.4.3, 2.5:

http://www.python.org/doc/<version>/whatsnew/

[Gregory Piñero]

Thanks guys, and now the world knows:
http://www.answermysearches.com/index.php/super-easy-way-to-reverse-a-string-in-python/188/

Well my 3 blog readers or the world ... not sure.

-Greg

[Fredrik Lundh]

p.la...@ieee.org wrote:

> That 'foo'[::-1] is the Python reverse string idiom I'll try here
> forward, thanks.
>
> Also '.h.e.l.l.o'[1::2] to pick out every second char, etc., thanks.
>
> Three footnotes:
>
> 1) Reverse string isn't yet in http://www.python.org/doc/faq/

so what are you waiting for?

http://pyfaq.infogami.com/

> 2) Google Groups searches here yesterday instead pushed me towards the
> less concise:
>
> def reverse(chars):
> aa = array.array('c', chars)
> aa.reverse()
> return aa.tostring()

that's a reasonably efficient way to do this in older versions.

</F>

[p.la...@ieee.org]

> http://pyfaq.infogami.com/

Tell me more?

Clueless newbie me, thru this door I'm at three deaths and counting.
Does that Py Faq Wiki have a sandbox a la alt.test, and/or a tutorial?

// Death One:

http://pyfaq.infogami.com/_account/in?path=/
requires me to create a persisting ID "between 3 and 20 letters and
numbers", i.e., not an e-mail address. Grumble, ok.

// Death Two:

http://pyfaq.infogami.com/programming-index
kicked back comment "How can I reverse a string, an array, a list,
etc.?" with "Sorry, that looks like spam. I'm not going to post it."

// Death Three:

Search infogami in clp gives me:
http://howto.infogami.com/createnewpages
which suggests:
http://pyfaq.infogami.com/how-do-i-reverse
which dies at "Sorry, that page could not be found."

//

Next clue?

[Georg Brandl]

p.la...@ieee.org wrote:
>> http://pyfaq.infogami.com/
>
> Tell me more?
>
> Clueless newbie me, thru this door I'm at three deaths and counting.
> Does that Py Faq Wiki have a sandbox a la alt.test, and/or a tutorial?
>
> // Death One:
>
> http://pyfaq.infogami.com/_account/in?path=/
> requires me to create a persisting ID "between 3 and 20 letters and
> numbers", i.e., not an e-mail address. Grumble, ok.
>
> // Death Two:
>
> http://pyfaq.infogami.com/programming-index
> kicked back comment "How can I reverse a string, an array, a list,
> etc.?" with "Sorry, that looks like spam. I'm not going to post it."

I must say that this has also happened to me before. Fredrik, is there
some description of what infogami regards as spam? Do comments have to
have a minimum length?

That said, hasn't it worked well in the past to use no spam filter, if
you have to be registered to post comments?

Georg

[Fredrik Lundh]

p.la...@ieee.org wrote:

> Next clue?

I would have hoped that the suggestion links on the first page would have sent
you to

http://pyfaq.infogami.com/suggest

which is the "right" place to submit new entries. that spam thing looks weird,
though; guess I'll have to check with Aaron.

</F>

[p.la...@ieee.org]

> http://pyfaq.infogami.com/suggest

> is the "right" place to submit new entries.

Thanks for sharing the secret. Now there I have added: "Q: How can I

reverse a string, an array, a list, etc."

And to share our secret with future newbies, to
http://pyfaq.infogami.com/ I've added the suggestion:

///

How about here we add a bold:

If you have a suggested FAQ, click thru the Suggest New Articles link
and add a comment there. Don't choose the relevant category and then
discover you lack the privilege to comment there. Don't give up because
you have no ID: just invent one and register your e-mail and proceed.

///

> I would have hoped that the suggestion links on the first page would have sent you

I actually did visit the right place - it appears listed as only the
fourth "resource" behind the label "Suggest New Articles". But the
only suggestions that were FAQs were from the effbot and submitted with
a font I didn't know how to create. Also I had no sure idea of what
"resource", "category", and "article" meant in this context, so I could
barely decipher that only-apparently-English page.

Instead, because the site looks like a Wiki, I was trying to add my
suggested FAQ in place in the relevant category. The place I picked
that choked irrecoverably was the "Programming FAQ" category, just
ahead of the "How do I modify a string in place?" question, in between
the "How do I convert a string to a number?" and "How do I convert a
number to a string?" questions.

Pat LaVarre

[Fredrik Lundh]

p.la...@ieee.org wrote:

> Thanks for sharing the secret. Now there I have added: "Q: How can I
> reverse a string, an array, a list, etc."

thanks! I'll take another look at the texts and the site settings when
I find the time (still waiting for the infogami folks to get back to me
about the spam filter...)

</F>