Inserting colon in a string

[vipul borikar]

Hi list,

          I want to convert a hex string in colon separated string like this:

str1 = 0x21000024ff3afd2b   output = 21:00:00:24:ff:3a:fd:2b

I tried something like this:

###########################
output = output[2:]
               
li = list(output)
               
count = 2

while count < len(li):
   
         li.insert(count, ':')
   
         count += 3
   
print "".join(li)
################################

The above code looks little messy.

Anybody has any better idea to do it?

--

Thanks 

Vipul Borikar

"Our task must be to free ourselves...by widening our circle of compassion to embrace all living creatures and the whole of nature and its beauty."

[Dhananjay Nene]

input = "0x21000024ff3afd2b"

assert(":".join(input[i:i+2] for i in range(2, len(input), 2)) == "21:00:00:24:ff:3a:fd:2b")

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[Dhananjay Nene]

If you wanted to be particularly picky about performance (not required in most cases)

def pairs(s):

    try :

        i = iter(s)

        while True :

            c1 = next(i)

            c2 = next(i) 

            yield c1 + c2

    except StopIteration :

        pass

    

assert(":".join(pairs("0x21000024ff3afd2b"[2:])) == "21:00:00:24:ff:3a:fd:2b")    

[Anand Chitipothu]

On Tue, Apr 30, 2013 at 8:35 PM, Dhananjay Nene <dhananj...@gmail.com> wrote:

If you wanted to be particularly picky about performance (not required in most cases)

def pairs(s):

    try :

        i = iter(s)

        while True :

            c1 = next(i)

            c2 = next(i) 

            yield c1 + c2

    except StopIteration :

        pass

    

assert(":".join(pairs("0x21000024ff3afd2b"[2:])) == "21:00:00:24:ff:3a:fd:2b")    

I don't think this will be any faster than the earlier implementation.

Just for fun, here is another approach.

def pairs(s):

    return (a+b for a, b in zip(s[::2], s[1::2]))

assert(":".join(pairs("0x21000024ff3afd2b"[2:])) == "21:00:00:24:ff:3a:fd:2b")    

Anand

[steve]

Hi,

On Tuesday 30 April 2013 09:42 PM, Anand Chitipothu wrote:
>
> On Tue, Apr 30, 2013 at 8:35 PM, Dhananjay Nene <dhananj...@gmail.com
> <mailto:dhananj...@gmail.com>> wrote:
>
> If you wanted to be particularly picky about performance (not required in
> most cases)
>
> def pairs(s):
> try :
> i = iter(s)
> while True :
> c1 = next(i)
> c2 = next(i)
> yield c1 + c2
> except StopIteration :
> pass
>
> assert(":".join(pairs("0x21000024ff3afd2b"[2:])) == "21:00:00:24:ff:3a:fd:2b")
>
>
> I don't think this will be any faster than the earlier implementation.
>

Actually, it is significantly faster:

>>> def pairs(s):
... try :
... i = iter(s)
... while True :
... c1 = next(i)
... c2 = next(i)
... yield c1 + c2
... except StopIteration :
... pass
...
>>> timeit.timeit('pairs("0x21000024ff3afd2b")', setup='from __main__ import
pairs')
0.7603280544281006
>>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))',
setup='s="0x21000024ff3afd2b"')
4.8088250160217285
>>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )",
setup='s="0x21000024ff3afd2b"')
6.071056127548218
>>>

cheers,
- steve

[steve]

On second thoughts ...

^^^^^^^^^^^^ this just creates the generator object ...my bad, so the revised
test is:

> 0.7603280544281006
> >>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))',
> setup='s="0x21000024ff3afd2b"')
> 4.8088250160217285
> >>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )",
> setup='s="0x21000024ff3afd2b"')
> 6.071056127548218
> >>>
>

>>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"[2:]))', setup='from
__main__ import pairs')
9.683159828186035

...which is actually worse. hmm, interesting.

cheers,
- steve

[Dhananjay Nene]

Thanks steve for setting up an interesting observation. 

Yes, it is peculiar. I defined another function pair2 (which had a minor change compared to pair) 

def pairs2(s):

    try :

        i = iter(s)

        while True :

            yield next(i) + next(i)

    except StopIteration :

        pass

I was just trying to avoid creation of two temporary variables here.

On Python 2.7.3 I got

>>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"))', setup='from __main__ import pairs')

4.479202032089233

>>> timeit.timeit('":".join(pairs2("0x21000024ff3afd2b"))', setup='from __main__ import pairs2')

4.3042449951171875

>>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))', setup='s="0x21000024ff3afd2b"')

1.9831359386444092

>>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )", setup='s="0x21000024ff3afd2b"')

2.999051809310913

On Python 3.3.0, the results I got were :

>>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"))', setup='from __main__ import pairs')

4.570932610997261

>>> timeit.timeit('":".join(pairs2("0x21000024ff3afd2b"))', setup='from __main__ import pairs2')

4.241085749999911

>>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))', setup='s="0x21000024ff3afd2b"')

3.5848920159987756

>>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )", setup='s="0x21000024ff3afd2b"')

3.166921207000996

Whereas on PyPy 1.9 (Python 2.7.2) I got

>>>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"))', setup='from __main__ import pairs')

0.845271110534668

>>>> timeit.timeit('":".join(pairs2("0x21000024ff3afd2b"))', setup='from __main__ import pairs2')

0.7255899906158447

>>>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))', setup='s="0x21000024ff3afd2b"')

0.626521110534668

>>>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )", setup='s="0x21000024ff3afd2b"')

2.3363211154937744

Go figure it out for what it is worth :)

[steve]

Hi Dhananjay,

On Tuesday 30 April 2013 10:23 PM, Dhananjay Nene wrote:
>
> ....[snip]...

> Thanks steve for setting up an interesting observation.
> Yes, it is peculiar. I defined another function pair2 (which had a minor change
> compared to pair)
>
> def pairs2(s):
> try :
> i = iter(s)
> while True :
> yield next(i) + next(i)
> except StopIteration :
> pass
>
> I was just trying to avoid creation of two temporary variables here.
>
> On Python 2.7.3 I got
>
> >>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"))', setup='from __main__
> import pairs')
> 4.479202032089233
> >>> timeit.timeit('":".join(pairs2("0x21000024ff3afd2b"))', setup='from
> __main__ import pairs2')
> 4.3042449951171875
> >>> timeit.timeit('":".join(s[i:i+2] for i in range(2, len(s), 2))',
> setup='s="0x21000024ff3afd2b"')
> 1.9831359386444092
> >>> timeit.timeit("':'.join( a+b for a, b in zip(s[::2], s[1::2]) )",
> setup='s="0x21000024ff3afd2b"')
> 2.999051809310913
>
>

I have a feeling this has something to do with the function call overhead, because:

>>> timeit.timeit('":".join(pairs("0x21000024ff3afd2b"[2:]))', setup='from
__main__ import pairs')

9.249284982681274
>>> timeit.timeit('":".join(pairs2("0x21000024ff3afd2b"[2:]))', setup='from
__main__ import pairs2')
9.641417026519775
>>> timeit.timeit("':'.join( next(i) + next(i) for _ in s[2:] )",
setup="s='0x21000024ff3afd2b'; i = iter(s[2:])")
2.451604127883911
>>>

cheers,
- steve

[Dhananjay Nene]

I have a feeling you just nailed it :)

[steve]

Hi,

Although unrelated to the OP's question, what bothers me is this tho' ...
On Tuesday 30 April 2013 10:41 PM, Dhananjay Nene wrote:
> [ ...snip ...]

>
>
> On Tue, Apr 30, 2013 at 10:40 PM, steve <st...@lonetwin.net
> <mailto:st...@lonetwin.net>> wrote:
> >>> timeit.timeit("':'.join( next(i) + next(i) for _ in s[2:] )",
> setup="s='0x21000024ff3afd2b'; i = iter(s[2:])")
> 2.451604127883911
> >>>
>
>
> I have a feeling you just nailed it :)
>

>>> s = "0x21000024ff3afd2b"
>>> i = iter(s)
>>> for x in range(10000):
... next(i)
...
'0'
'x'
'2'
'1'
'0'
'0'
'0'
'0'
'2'
'4'
'f'
'f'
'3'
'a'
'f'
'd'
'2'
'b'
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
StopIteration
>>> ''.join(next(i) for _ in range(10000))
'0x21000024ff3afd2b'

Is that (not raising a StopIteration) valid (ie: defined) behaviour ?

cheers,
- steve

[Dhananjay Nene]

We have a clear winner at least from a perf perspecive

s='0x21000024ff3afd2b'; i = iter(s[2:])

':'.join( next(i) + next(i) for _ in s[2:] )

Beats all the other options quite handsomely across 2.7.2, 3.3.0 and pypy 1.9 (python 2.7.2)

[steve]

sorry I didn't copy past the obvious:
>>> i = iter(s)

between the two

[vipul borikar]

Thanks everyone for the interesting replies...

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