Creating formatted output using picture strings

Arnaud Delobelle arnodel at googlemail.com
Wed Feb 10 19:21:35 CET 2010


python at bdurham.com writes:

> Original poster here.
>
> Thank you all for your ideas. I certainly learned some great techniques
> by studying everyone's solutions!!
>
> I was thinking that there was a built-in function for this common(?) use
> case which is why I shied away from writing my own in the first place
> ... hoping to not-reinvent the wheel, etc.
>
> Here's the solution I came up with myself. Its not as sexy as some of
> the posted solutions, but it does have the advantage of not failing when
> the number of input chars <> the number of placeholders in the pic
> string. I think it handles the edge cases pretty elegantly unless I'm
> too close to the details to miss the obvious.
>
> Any feedback on what follows would be appreciated.
>
> # format s using a picture string 
> # stops processing when runs out of chars in s or pic string
> # example: picture("123456789", "(@@@)-@@-(@@@)[@]")
> def picture( s, pic, placeholder="@" ):
>     s = list( s )
>     output = []
>     for sym in pic:
>         if sym <> placeholder:
>             output.append( sym )
>         elif len( s ):
>             output.append( s.pop( 0 ) )
>         else:
>             break
>     return ''.join( output )
>
> # test cases
> print picture("123456789", "(@@@)-@@-(@@@)[@]")
> print picture("123456789ABC", "(@@@)-@@-(@@@)[@]")
> print picture("1234", "(@@@)-@@-(@@@)[@]")
> print picture("123456789", "(@@@)-@@-(@@@)")
> print picture("123456789", "(@@@)-@@-(@@@)[@][@@@@@]")
> 	
> Regards,
> Malcolm

def picture(s, pic, placeholder='@'):
    nextchar=iter(s).next
    return ''.join(nextchar() if i == placeholder else i for i in pic)

passes all your test cases I think (I can't be sure because you didn't
post the expected output).  The trick is that when nextchar reaches the
end of the string 's', it raises a StopIteration which is caught by the
generator expression.

-- 
Arnaud



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