list comprehension

[Guy Robinson]

s.replace(',',',-') HA!!:-)

Thanks Andrew. As usual making it more complicated than it needs to be...

Guy

Andrew Bennetts wrote:
> On Mon, May 10, 2004 at 12:32:20PM +1200, Guy Robinson wrote:
> 
>>Hello,
>>
>>Trying to change a string(x,y values) such as :
>>
>>s = "114320,69808 114272,69920 113568,71600 113328,72272"
>>
>>into (x,-y):
>>
>>out = "114320,-69808 114272,-69920 113568,-71600 113328,-72272"
>>
>>I tried this:
>>
>>print [(a[0],-a[1] for a in x.split(',')) for x in e]
>>
>>But it doesn't work. Can anyone suggest why or suggest an alternative 
>>way? The text strings are significantly bigger than this so performance 
>>is important.
> 
> 
> It has several syntax errors; (a[0],-a[1] for a in x.split(',')) is not a
> valid expression because list comprehensions are bracketed by square
> brackets, not parentheses.  Also, the first part of a list comprehension,
> the expression to calculate each element, needs to be in parens to if it has
> a comma, so that the parser can disambiguate it from an ordinary list.
> 
> I also don't know where you got 'e' from.  Is it 's', or 's.split()'?
> 
> If list comprenhensions grow unwieldy, just use a for loop.  They're
> probably easier to read than a list comprehension that takes you ten minutes
> to concoct, and performance is almost identical.  For the sake of answering
> your question, though, here's a expression that does what you ask:
> 
> 
>>>>s = "114320,69808 114272,69920 113568,71600 113328,72272"
>>>>s.replace(',',',-')
> 
> '114320,-69808 114272,-69920 113568,-71600 113328,-72272'
> 
> You could do this with list comprehensions, e.g.:
> 
> 
>>>>' '.join(['%s,-%s' % tuple(x) for x in [pairs.split(',') for pairs in s.split(' ')]])
> 
> '114320,-69808 114272,-69920 113568,-71600 113328,-72272'
> 
> But I don't really see the point, given the way you've described the
> problem.
> 
> -Andrew.
> 
>