list comprehension

[Guy Robinson]

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.

TIA,

Guy