Re: [Tutor] Splitting a number into even- and odd- numbered digits

2006-04-20 Thread Carroll, Barry 
Greetings:

Unfortunately, my problem description was incomplete.  I forgot to
include two important requirements:

1. the length of the input string is arbitrary,
2. the order of the digits must be maintained.

I could not find a way to include these requirements in a single, simple
expression.  I decided to make an explicit test for string length, which
simplified matters. I came up with this:

>>>
>>> def odd_even(x):
... if len(x) % 2 == 1:
... return x[::2], x[1::2]
... else:
... return x[1::2], x[::2]

>>> odd_even('987654321')
('97531', '8642')

>>> odd_even('98765432')
('8642', '9753')
>>> 
>>>

which is an improvement, I think, on my original.  
 
Thanks to those who provided suggestions.  This is the most useful list
I've ever found.

Regards,
 
Barry
[EMAIL PROTECTED]
541-302-1107

We who cut mere stones must always be envisioning cathedrals.

-Quarry worker's creed


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Re: [Tutor] Splitting a number into even- and odd- numbered digits

2006-04-20 Thread Carroll, Barry 
Greetings:

First of all, thanks to those who contributed suggestions.  

Unfortunately, my description was incomplete.
 
> I am writing a function that accepts a string of decimal digits,
> calculates a checksum and returns it as a single character string.
> The first step in the calculation is to split the input into two
strings:
> the even- and odd- numbered digits, respectively.  The least
significant
> digit is defined as odd.
 
I forgot to include two important requirements:

1. the length of the input string is arbitrary,
2. the order of the digits must be maintained.

I could not find a way to include these requirements in a single, simple
expression.  I decided to make an explicit test for string length, which
simplified matters. I came up with this:

>>>
>>> def odd_even(x):
... if len(x) % 2 == 1:
... return x[::2], x[1::2]
... else:
... return x[1::2], x[::2]

>>> odd_even('987654321')
('97531', '8642')

>>> odd_even('98765432')
('8642', '9753')
>>> 
>>>

which is an improvement, I think, on my original.  
 
> >>>
> >>> s = '987654321'
> >>> odd = ''
> >>> for c in s[::-2]:
> ... odd = c + odd
> ...
> >>> s = s[:-1]
> >>> even = ''
> >>> for c in s[::-2]:
> ... even = c + even
> ...
> >>> odd
> '97531'
> >>> even
> '8642'
> >>>
 
Thanks again.  This is the most useful list I've ever found.

Regards,
 
Barry
[EMAIL PROTECTED]
541-302-1107

We who cut mere stones must always be envisioning cathedrals.

-Quarry worker's creed


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Re: [Tutor] Splitting a number into even- and odd- numbered digits

2006-04-20 Thread Python 
On Wed, 2006-04-19 at 17:17 -0700, Carroll, Barry wrote:
> Greetings:
> 
> I am writing a function that accepts a string of decimal digits,
> calculates a checksum and returns it as a single character string.  
> The first step in the calculation is to split the input into two
> strings: the even- and odd- numbered digits, respectively.  The least
> significant digit is defined as odd.  
> 
This sounds like credit card checksum processing.  This is my code for
that:

def isbad(cardnumber):
factors = ([2,1] * 8)[-len(cardnumber):]# alternating factors of 2 
and 1 ending with 1
chkprods = [int(d)*f for (d,f) in zip(cardnumber,factors)]
return sum(chkprods) % 10

This deviates quite a bit from your description and the description of
the algorithm that I was working from.  It was only after I had coded up
separate even/odd character lists and looked at what was going on that I
realized there was a much simpler way to describe the rules.

Hopefully, I am not off in left field here.

> The following code fragment does the job but seems sort of brutish and 
> inelegant to me:
> 
> >>>
> >>> s = '987654321'
> >>> odd = ''
> >>> for c in s[::-2]:
> ... odd = c + odd
> ... 
> >>> s = s[:-1]
> >>> even = ''
> >>> for c in s[::-2]:
> ... even = c + even
> ... 
> >>> odd
> '97531'
> >>> even
> '8642'
> >>>
> 
> Is there a better (i.e. more Pythonic) way to do this?  
> 
> Thanks in advance for all your help.
> 
> Regards,
>  
> Barry
> [EMAIL PROTECTED]
> 541-302-1107
> 
> We who cut mere stones must always be envisioning cathedrals.
> -Quarry worker's creed
> 
> 
> ___
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-- 
Lloyd Kvam
Venix Corp

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Re: [Tutor] Splitting a number into even- and odd- numbered digits

2006-04-19 Thread John Fouhy 
On 20/04/06, Carroll, Barry <[EMAIL PROTECTED]> wrote:
> The following code fragment does the job but seems sort of brutish and 
> inelegant to me:
>
> >>>
> >>> s = '987654321'
> >>> odd = ''
> >>> for c in s[::-2]:
> ... odd = c + odd
> ...
> >>>

String slicing will actually produce strings :-)

eg:

>>> s = '987654321'
>>> s1, s2 = s[::-2], s[-2::-2]
>>> s1
'13579'
>>> s2
'2468'

--
John.
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